I carry mine quite often and keep it loaded with 38 Special +P ammo. I've found 357 Magnum rounds are not my preferred ammo due to the added recoil, blast, and flash. If I carry it in the woods I will load it with 357 Magnums, just not for daily carry.
Although heavier than the airweights, the steel J frames make for better shooters recoil-wise. The 640 Pro's moon clips can make reloads easier.
My picture shows it with wooden stocks, but it now is sporting Crimson Trace laser grips which originally came on my 642CT. The CT grips aren't as nice to look at, but they are better for recoil and the laser is a bonus.
I'll say the night sights are a big improvement over stock J frame sights. However, I find the dot size balance is off from front to rear.
When shooting, the rear dots appear much larger than the front... Just the opposite of what I want. I have modified the daytime sight picture by putting orange paint on the front sight post around the tritium dot. Now it is a little quicker for me to get sights on target.
Eliminating the white outline from the rear tritium dots could help. If I were on the design team I would have made it a dot-over-dot system. White or orange outlined tritium up front and a no-outlined tritium spot under the rear sight notch. So close to perfection, yet missed it by this much. Minor issue...
S&W will often not show pics of the left side of their wheel guns. It is almost as if there is something embarrassing over on that side! As mentioned before, this gun is a 640-1 and has no internal lock (I'm not afraid to take a left-side pic). I really think they wanted the picture to show both the "Pro Series" and ".357 Mag" etchings which are on the right side.
The biggest problem with the 640 Pro is availability. That, and with my gun it was current production quality assurance. Mine had to go back to the mothership twice for numerous problems which should never have left the factory.
Before you pull out your hard earned $$$ look the gun over. Things like barrel to frame alignment, etchings, and general fit and finish.
Overall, this is a nice J frame for carry. Good recoil management because of the all steel weight, if needed it is capable of shooting 357 Magnums, better sights than the standard J frame, and the moon clip option if you want it. Not a bad package...
Sorry for the ramblings...
Edmo