Some people don't like the plastic mags for two reasons:
* under heavy use in the gun, they can get soft (Thermelts), but I haven't heard of it in a semi-auto gun. But there are rumors about heavy use of select-fire M16's.
* if dropped on a hard surface while loaded, they could crack making them unusable...while the USGI's are better in this respect.
Thermolds fit in the Bushmasters fine. It's the Orlites you have to watch out for. Some Orlites have some ridges too high to fit in the Bushmaster. Five minutes with a Dremel will fix it. Or you can just look for a number code on the Orlite magazine...it's at the bottom of the mag inside a circle...like this:
We're not concerned about the zero...only the other number. If it's 20 or above, then you're OK (the lower numbers fit the Galil rifle better). I have some "26's" and some "32's" that work great.