The Walther PP, PPK and PPK/S are all steel framed guns. I believe there was an alloy framed variant, but that one would be rare and a collector's item.
The Walther PP series guns are beautifully balanced, point well and carry well. They are slim, but not super light. The weight isn't a bad thing when shooting...recoil with the .380 in a blowback action gun like the PP series, is snappy.
The design dates back to the 1920s and was way ahead of its time. As I undestand it, it was the first successful double action design. With a round in the chamber, pulling the trigger discharges the gun. It's blowback operation ejects the spent case, chambers the next round and cocks the weapon, leaving it in single action mode for the remaining shots.
Note that blowback operation is not identical to recoil operation and is only suitable for rounds like the .22, .32 and .380 (which are the chamberings for Walther PP series; I have read that the .32 is more pleasant to shoot then the .380). Blowback action is not considered as reliable as recoil operation.
Historically, the PP was the first model. It has a slightly longer barrel and grip frame then the more compact PPK. The PPK/S is a blend--it has the same frame as the PP, but the same slide/barrel as the PPK. The PPK/S was a variant developed to allow import even after the 1968 gun control act.
Mag capacity on the PPK is 6; the PPK/S is 7 and the PP is 7, in .380ACP.
The grips on the PP and PPK/S do NOT cover the backstrap. However, the PPK's grips DO cover the backstrap (the backstrap area of the PPK's grips actually cover the mainspring, a design variation from the PP and PPK/S). I carried a Walther PPK/S .380ACP extensively (concealed). I shot it a lot, too. My hands are hard on blue steel guns and the blue really wore off on that exposed backstrap. So, in terms of finish preservation, I like the PPK's closed backstrap design.
The double action trigger pull is typically heavy. Single action is crisp and very nice.
Sights are small, often offered with the three dot pattern.
Walther manufactured the PP series until the end of WWII. Post war production was carried out by Manurhin in France, under license of Walther. Eventually, Walther began manufacturing the guns in Germany again. German made Walthers are the most desirable. In the 1980s/90s, Interarms, under license of Walther, manufactured the PPK and PPK/S in blue and stainless steel in the US. These guns are the same, design wise, as the original German guns. If it's a stainless PPK or PPK/S, it was made in the USA. Quality control of the US made Interarms guns seems to vary.
In recent years, S&W has manufactured the Walther PPK and PPK/S in the US under license of Walther. The S&W made guns deviate somewhat from the classic design...for instance, the tang is slightly longer, to prevent hammer bite (a common problem for many shooters with the original design). The S&W made guns seems a little thicker then the classic Walther. The S&W PPK and PPK/S have had recalls and I've heard, on the Internet, complaints. I have no personal experience with them myself.
My PPK/S is an Interarms' US made gun from '89. It is reliable when using hot loads (mild loads resulted in stove pipe jams). Select a load (particularly for defense) that really cycles that slide. My wife has a US made PPK that has been reliable and even has an unusually good double action trigger. It's quite accurate.
As you know, "limp-wristing" will aggravate reliabiliity problems with all semi autos--and particularly so with blow back action semi autos. Keep the wrist locked!
Since German made PPKs available in the US are all pre-1968, they will be pricey and more of a collector's item. The German PPK/Ss were imported after '68, but are expensive items, too. Plus, I don't know how these vintage guns would fare with modern duty ammo. Some gunsmithing might be needed. But they will be very fine guns--I have a German made PP from the '60s that is finer in over all fit and finish then my US made PPK/S.
I have no personal experience with the Manurhin guns.
As with the Beretta 92, the Walther PP series has a slide mounted safety catch, which will also serve as a decocker. It is small and difficult to flip up...particularly under the stress of a gunfight. In a gunfight, you may be injured and the hands may be bloody. I'd hate to have flip that tiny safety in such a situation.
The alternative is to carry the weapon with the safety off. However, if dropped in this condition, the gun may discharge.
So, of the PP series guns, which one to select? Personally, I'd go with .380 PPK in blue steel. I would consider replacing the stock plastic grips with wood made by Nill Grips. However, the stock grips are serviceable. My first choice would be a German made PPK. Second choice would be a US made, Interarms PPK, preferably new in the box. I would pass on the S&W and the Manurhin, due to lack of personal experience.
However, if your chief wants a brand new gun, the S&W is the only game in town...so hopefully you'll get some good information on this forum concerning it.
For a carry gun, I prefer the PPK over the PPK/S and PP only because it conceals slightly better. As I have medium/small hands, the PPK is not too small for me. If I just wanted a shooter for the range, I might prefer the PP, which is a little more most pleasant, due to its additional weight and size. It also points very, very well.
As a carry gun, your chief might prefer the PPK/S if his hands are larger. An extra round doesn't hurt, either. With either model, to improve concealment, you can use a magazine with a flat floor plate, instead of the spur type. If carried on the ankle, I would go with the flat floor plate. The US made Interarms guns offered one of each with the pistol. I'm not sure about the S&W.
I personally prefer blue over stainless steel. I have heard that the blue guns are more reliable, but don't know if that's true or not. But if I'm going to carry a classic like the PPK, let it look like it belongs in a shoulder rig under a dinner jacket.
By the way, since the PPK is often chosen because of the James Bond connection, and a shoulder holster is desired, there is none better than the elegant and totally practical one made by Andy Arratoonian, of Horseshoe Leather, in England. You easily can order on line. He is a true master and makes every holster himself.
Now, with all that said, since I assume we are talking about a gun for LE work...allow me to suggest what I consider to be a better .380 alternative: the excellent Sig Sauer P232 (or its predecessor, the P230). It is chambered in in .380, and may be had in blue (w/alloy frame) or in stainless steel. Similar in design to the PPK. It's slightly larger then the PPK, but the blue version is lighter. Overall size of the Sig is comparable to the PP. The Sig is elegant and visually and mechanically similar to the Walther PP series guns.
Like the Walther, the Sig is a blowback action and its barrel is fixed to the frame. Dissasembly is similar, but not the same. With the Walther, the trigger guard is disengaged from the frame before the slide is lifted off. With the Sig, a frame mounted lever is turned, then the slide is lifted off.
Like the Walther, the Sig does not have a slide lock release lever. It locks open on an empty chamber. With the slide locked to the rear and a loaded mag is in place, the slingshot method is used to chamber a round.
The P232 uses a frame mounted decocker (like the Sig P220 series). It's safe to carry with a round in the chamber, hammer down. There is no manual safety on the P232(internal safeties prevent discharge if dropped). Magazine capacity is 7 rounds. The mags have a modest spur style floor plate. Grips are plastic and serviceable. If wood is prefered, Karl Nill grips wood grips are excellent.
Double action trigger pull is reasonable and single action is excellent. The Sig P232/230 has great handling characteristics, is accurate, reliable and is very well made...and it's still made in Germany. I am one who believes the German made Sigs have better quality control than the American manufactured Sigs.
One potential issue with the Sig P232/230--it uses the European style heel release for the magazine, like the Walther P-38. The Walther PP series guns have the mag release button in the famililar American location. Personally, I don't have an issue with the European heel release...but some do.
Bottom line: if I was going into harm's way with a .380 (Heaven forbid), it would be the Sig P232 or P230. If selecting a .380, I would also prefer the Sig over the latest micro pistols from Smith, Ruger, et al, as I have no experience with them.
I would go with a premium hollow point that was reliable and accurate in my weapon. I like the Remington Golden Saber 102 grain, one of the heavier weight loads in .380.
Last thought: Your chief maybe nostaligic for his old Walther, or he might really like the idea of the James Bond gun. Lord knows, I do. But, if we're talking about a small life saver when the chips are down, it's hard to beat a Smith J frame in .38 special...or a Glock 26 or 27 in 9mm or .40. But that's another discussion!
If he has his heart set on a Walther PPK and is willing to spend the money, find one of those mint German ones that turn up now and then.
If you've read this far and haven't fallen asleep, thanks for listening and I hope it was useful information.