Yeah, originally the FS990 was for the front as I recall - different cable clamps and stuff.
They are better than Tektros, they don't flex as much. however, clean rims, the right blocks, nicely adjusted springs and oiled cables make all the difference really. I'm running ADs on my bike now, the stock green blocks are too hard for the rear at least. I bought some Clarks blocks from Halfrauds (£6 a pair) and whacked them on, jobs a goodun
For your info, ADs, FSs, Hombres are basically just all dirivatives (sp) of the good old AD.