The FEGs can get complicated. The early ones I was told were actually built with old FN tooling and are true clones, although the interior finishing was a bit rougher. But FEG made multiple variations, some of which use a modified S&W type barrel lug, so you have to check which version it is. I have one of these from the 70's, and it's exactly like a pre-Mark II High Power.
The Arcus 94 is internally like a high power, people generally report that all internal parts interchange, but the frame and slide dimensions are not quite the same, they are really thickened up and squared. The slide in particular is really thicker than a high power. They have a reputation for being able to take +P rounds very well, though, so you do get some benefit from the blockyness. I have a detective length model. It's boxy, but good. Most seem to have an extended beavertail making slide bite impossible. It's not elegant looking like the real High Power shape, but I like knowing I can safely load the most powerful ammo I might desire.
Kareens- I've not seen the Mark I, but have seen the Mark II.
All of these should use the standard High Power Mags.
The Mark I Kareen was made by FEG, and seems to generally be the exact clone like my FEG- but check carefully, cause it might not be unchanged.
The Mark II Kareen seems to have been made by Arcus (JMO from seeing one) and looks like an Arcus 94 machined closer to High Power lines. They look just a bit thicker than a true High Power, but lines are much closer to the original, more or less keeping the curves. Some have an extended beavertail. I've held one, it was solid workmanship, but not fancy or finely finished.