I have a new Olympic A3-just swapped a Colt A2 for it. I like the Oly more since it shoots common steel cased ammo better than the Colt did. Accuracy is good with proper ammo. I've shot MFS brass case, boxer primed FMJ and Hornady steel cased SST besides some handloads. Not a one hole shooter but definately under 1.5" and some much less.
Mag availability is problematic(especially right now) but C-Products(now ASC) mags work well. They show up here and there. I had some "Frankenmags"(AR upper body TIG welded to an AK lower part) but sold them years ago when the C-P mags started showing up in useable numbers. Current prices are all over the place and careful shopping is imperative.
As far as compatability, it depends on the individual upper/lower. Some will pin together w/o issue. Some will be a little sloppy. Some will be so tight as to require a little "adjusting" before the pins will insert.