I put them on my KX with a Renthal RK1 chain about 2 months ago. So far so good. A friend put the same combination on his RM250 last winter and he is still running them with no problems.
I ordered a steel rear sprocket and it rounded the teeth on the first ride, they sent me out another and it did the same thing. I dont think they got hardened or something. Personally I would go with Sprocket Specialists alum, they have held up well for me and my buddies.
If the teeth of your sprockets kept rounding it is probably because you are using a worn out chain. Always start fresh with new chain and sprockets for best wear. And realistically, a lower priced steal sprocket will out last an alluminum one. Ever wondered why they don't make alluminum counter shaft sprockets?