I have used their cassettes, they are just fine and worth the savings, in my opinion. More importantly, at least when I last looked, they had more options in 6 and 7 speeds than did Shimano.
I am not so thrilled with their bottom brackets, however. They are dirt cheap, and I have used them because of that, but run raw way quicker than any cartridge bb should. I think investing a bit more is worth it here.