dlcra:
The Remington 870 is indeed a good choice as a home defense weapon. Keep it handy

....
The M&P40C is a little chubby compared to a lot of single-stack .40's, but is roughly the same thickness as your average 1911 (in .45ACP). I don't find shooting either the 40C or 40FS particularly difficult, but I'm a 1911 guy, so as long as the gun isn't trying to hurt me, the extra "kick" from the .40 isn't a problem. (An M&P9C is a lot more fun to shoot, but I'm one of those guys who's happier with a ".4x"

.)
(I have a 9C - bought it for my daughter. Long story....)
SOME compacts have narrow grip frames and (worse for me) narrow triggers. I can live with the former, but a .40 is a little wicked. My pudgy fingers tend to wrap around narrow triggers, which causes a painful pinch with each shot. The Walther PPS (which isn't bad otherwise) in .40 was too uncomfortable to shoot. KelTec's P3AT is similarly uncomfortable in .380, but all but the larger ones are uncomfortable anyway for me. I can use a PPK/S comfortably enough, but it's nearly as big as the 40C (or 9C) so there's no gain there. (A PF9 is actually a better choice, but is a KelTec, which just doesn't make me feel too good. I spent a lot of time getting my P3AT behaving at all.... The M&P's all have wide triggers that don't pinch me....
I wouldn't recommend a Shield in .40S&W without spending some time on the range with one, first. While you don't have to make a career out of firing the thing on the range, you do need to shoot it enough to be comfortable with it, and that may be a little too much for some people. The 9mm version, though, ought to be very pleasant.
What to do with the .40C? Depends on where you live, perceived needs, etc. Superb nightstand or glovebox gun, for example, but some states get stupid about that in the vehicle, and kids around the house & such may make the nightstand an issue, although it's small enough to secure fairly well. IAC, don't ditch the 40C until you're sure about the other one.
Carrying? I wear a 40C or 40FS around the house. While I use (as anybody should) a good holster, both are light enough that any old belt seems to work adequately. "Outside", it's a small 1911 in another very good holster and a barrel-hoop of a belt. I can carry (and have carried) a full sized 1911 "outside" from time to time, or swapped gear to carry the 40FS. On vacation, the 40C comes with me....
There are two rules: Don't do the "gun of the month club", which means that anything you carry either works the same as your most commonly carried gun, or has
fewer buttons & such. IOW, a thumb safety on the 1911's v.s. none on the M&P's. It's a lot safer to
not find a control than to forget that it's there, or remember that it's backwards.
Second rule: Don't carry a gun you can't afford to lose. I call this an "airline travel gun", in that I've got only money invested in it, and wouldn't mind an insurance check (hopefully at the end of a flight) for it if somebody manages to give it wings. Or, should I have to use it, getting it back in any condition that I'd like may be difficult or impossible.
Regards,