I have a PC9GR - 9mm with ghost ring sights. The .40 S&W version is the PC4.
The PC carbines are great guns. Mine has been utterly reliable and is more accurate than I am. It's very, very fun to shoot, especially when fitted with a red dot scope.
They're fairly easy to strip & clean. As I recall, you need something like a small punch or paper clip, inserted into a hole on the spring guide rod, to hold the action in place in order break it down completely. It's actually a very simple procedure. Reassembly can be tricky when putting the action/barrel into the stock. The slide assembly must be in just the right position when the action is set into place in the stock, otherwise the slide locks in place and will not move. Once you get used to it, again, it's easy.
Overall, the gun is relatively easy to clean. The only difficulty I have is with the nooks & crannies of the receiver and stock; and that's only a problem when I decide to try and get it spotlessly clean.
Magazines are very plentiful, though the .40 mags only hold 11 rounds. I can't recall for certain if anyone makes a higher capacity magazine for the .40 cal. guns.
The price seems to be okay; about average. There's a few on GunsAmerica less than $400, but many more higher than $420. All of the ones on GunBroker seem to be a fair amount higher than $420. For what it's worth, CDNN has unissued trade-in PC4 carbines for $339.99.
As for it being a SHTF gun... I dunno.
Though it's a long gun, it's still only firing pistol caliber ammunition. Something in a rifle caliber would likely be better suited for that situation.
It is a good gun, though. If you want one, then by all means, go for it. I've been extremely pleased with mine and wouldn't trade it for anything.
Good luck!
Steve