I have a PC4 and 2 of my Uncles have the PC9's.
It is a fun to shoot, reliable, accurate carbine. The .40 takes p944/p94 .40s&w magazines that are a little hard to find and pricey, the .9mm takes the p85,p89,p95,p94 magazines that are more common and have extended capacity aftermarket mags available.
It does have a heavy trigger, but a clean break and like you said, it is like a heavier 10-22 so most of the controls are the same, charging handle, sights, safety are in the same location but the mag release and bolt release are not.
It is a bit of a pain to break down for cleaning, but for a plinking/varmint gun it can go a long time without but if it is a home defense gun or something that you might risk your life on then you would want to clean it more often.
It takes Ruger style scope rings but there are adapters out there that hook up a standard rail to the ruger mount location.