The Shield is an absolutely amazing firearm that is not only , in my normal speech, "awesome for CCW" and perfect as my "Dedicated Every-Day-Carry" gun, but it is like the team at Smith and Wesson literally custom engineered this gun to be the ultimate CCW firearm.
I cannot speak to the 40c but, having been using a Glock 23 not only for carry but as my "main gun" so to speak since Jan 2010, I still bought the Smith and Wesson M&P Shield 9mm for CCW and have absolutely loved it ever since.
It's not too small that you feel underarmed, you have enough capacity in enough caliber (and I chose the 9mm but you are apparently going ahead with the 40, so you definitely won't be feeling under-powered) and physically large enough to shoot like a 'real gun', not a pocket protector or last resort type of gun. Especially with you use the 8-rd mag with the extended grip. HOWEVER, it is NOT large enough to be cumbersome or bothersome IN THE LEAST, IN ANY WAY - and I did pocket carry it for the first month I owned it. In a $10.97 Walmart Blackhawk pocket holster ... and it worked fine, no one ever knew I was carrying, I still carried other things in my other pockets, in shorts and t-shirt in Florida heat etc.
But, having just got the Galco King Tuk IWB hybrid holster I ordered, I am now reaping the benefits of true concealed carry with a proper holster and everything is just gravy. I forget I am carrying it while walking the dog. .. and I walk my dog a lot. That is one of the reasons I actually bought the Shield. I was having trouble not only concealing my Glock 23 ( I am not a big guy at all) but toting the damned thing around. Especially when you have the loaded G23 w/ 13+1 rds, and two loaded mags also, the weight and size takes a toll on walking the dog day-in day-out. I tried an Alien Gear Holsters tuckable IWB hybrid holster ,and while it certainly helped and is a fine product, it didn't solve my problem - but the Shield not only solved the problem, it made me extremely happy and satisfied.
In fact I just got my gun back from the gunsmith today - I had him install my TruGlo TFO night sights and he amazingly turned it around in 24 hours (16-18 hours really!) when he has 2 mo. worth of work backed up. So I have my new Shield 9mm with the new TruGlo TFO tritium/fiber-optic day/night sights, in my new Galco King Tuk IWB hybrid holster, with 7+1 in the gun and 2 8rd extended magazines in special thigh pockets included on LA Police Gear pants and shorts. I feel like a million bucks because the gun is supremely comfortable and barely even noticeable. Oh yeah , to round out the package, I tried out a $12 Walmart leather belt... and it made a significant improvement over the Bear Grylls belt I had used previously.
Sorry for the long story - I just wanted you to know how happy I am with the Shield and how highly recommended it is, even from someone who won't ever give up my Glock 23 in .40 ... but I certainly will carry the Shield a lot more.