I purchased the 22 compact in Oct 2017. I liked it so much I bought another a few months later. Reason why I went with the M&P Compact 22 over others like Sig, Ruger, Walther, etc. is because of what you mentioned about quality. When I took down the different firearms I liked the build of the M&P the most. Even in the hand it feels like better quality. I prefer the traditional mag release placement vs the trigger guard style mag release found on it's Walther cousin. Plus features like a threaded barrel, even though I'l never use it, and an adjustable rear sight were nice touches.
My wife never shot in her life but I figured this would be a perfect starter pistol. She loves it. I'm left handed so being able to move the mag release was a plus for me. It also makes it easy to identify which is hers and which is mine.
I shoot Blazer ammo. Never had an issue, recoil is almost non existent and it's very accurate in this firearm. I've also fired Winchester, Remington and Federal ammo with no malfunctions. I read reviews about how the Sig was finicky when it came to ammo so that why I ruled them out. The crimps on the Remington were so bad I did have accuracy issues though.
I can't comment about the mags between the compact and full size being interchangeable. However I did buy 2 additional 10 rd mags, giving me 6 total. I wound up having an issue with one of the mags where it wasn't securing the round. Rather than trying to fix it myself, I contacted S&W about the issue and they sent me a new mag. I sent the defective one back. Customer service is important to me.
Shop around because there are deals out there. It was cheaper for me to order online and pay the FFL fee. Check out this deal. https://www.sportsmansoutdoorsuperstore.com/products2.cfm/ID/216883