Does the size and weight reduction of the MP9c cause it to be any harder to handle or less pleasant to shoot than the full size MP9? On the flip side, is the full size concealable enough that it is worth the extra size for comfort on the range? What kind of trade off exists in your experience?

I have no trouble concealing a full size M&P. You should go to a range that rents pistols and try both. If you shoot well with the compact, and you're concerned about the handle "printing" as you carry it concealed, then you have your answer. You can always use a FS mag with the sleeve to give you a larger grip surface. OTOH, if you shoot better with the FS, that becomes your better choice. Consistently placing the BBs where you want them should be your overarching goal; the rest will sort itself out. As I said earlier, concealing a FS M&P is not an issue.

It depends on who you are and where you live..
I am 5'9" and 140lbs. I live in Florida.. Logically I need the compact. In the summer when its shorts and T, I cant even use the mag with the finger rest. Yup, that flat plate makes the difference.
I'm sure I could find a way to carry a full size, but I like my style and I like being as comfortable as I can in the heat.

As far as being able to shoot a compact: I cant imagine it being that difficult to shoot the 9c. I have the 40c, and i find it very easy to control.
The only thing I cant wait to change is getting the new Talon grips when they come out for the M&P. The polymer is just.. well you know. I put skate board grip tape on the small backstrap (i usually use the med), and wow! The talon grips are going to make a very nice addition to the compact.

Sounds like I'll be getting an 9c and an xgrip. I'm 5'10, 240, also in FL. I can conceal quite a bit, but the xgrip appears to make it basically fullsize anyway.

The 9C is very pleasant to shoot. Right after shooting a 38 Ruger LCR, it feels like a 22LR.

I have owned the FS models of both (M&P 45 and M&P 9) and I much prefer the compact models, which I now have (the M&P45c and the M&P9c.) I have small hands, and they fit me much better. Well, I should say the FS models were not at all uncomfortable, but the compact models just seem to carry and handle better for me.

I own both the FS and C in 40 cal. Keep in mind if you have to use your weapon it'll probably be within a few feet so accuracy should not be a factor. The C conceals well using the Blackhawk Serpa Conceal Carry holster. I'm 5'10" and 260. I'm going to order the spacers for the holster to have the gun be held just a bit farther away from my overhanging belly.

I have the FS 9mm and mid size 45acp, but carry and conceal well. I did however shoot a compact at the indoor range recently and ordered one for my wife, she liked it as well. I will tell you I was very surprised as I can shoot the compact just as well as my full size. There maybe another compact on order.