Are they actually any good, or just token offerings. Some of them are a darn sight lighter than the cheap Avids that came with the bike.
Thinking XCRacer types.

I’ve got KCNC jobbies on both my rigid SS and my xc race bike in 160mm all around. Can stop when I need to and I haven’t died yet.

Cheap and half the weight, cake and eat it.

I’ve got KCNC 160mm rotors as well, they can deliver enough punch to take me over the bars so they’re fine in that respect, and they’ve only warped very slightly after a lot of ues; far, far better than my old Avids. Possibly the only downside is they’re not particularly hard waring, so if you’re heavy on your brakes you’ll have to replace them more often than some others, but for XC/AM riding they’re great.

Ashima airotors are a tenner each on merlin, decent weight saving if your Xc racing I guess. Mine have been on and off the bike in a fortnight though, not enough power and rear has already warped, that’s on my alpine 160 riding a lot of dh in the mud, on steep tracks and in the wet, I was asking a bit much of them I think (know), just fitted some ice tech rotors, 25g difference per end but I’ll take that as the extra material on the braking surface will no doubt come in useful!!!

I used to have some stans rotors , very light coated alloy.
They gave just about enough stopping power for cx race use but for day to day use were just scary

Very light though