I've never tried a knockoff but my furminator is AMAZING...I am shocked by how much fur I get off both my girls everytime I brush them (one is long hair and the other is short). So if you were less than impressed with the one you bought I would have to guess and say it is probablly not as good as the real thing...i've gotten several cat and dog friends completely hooked on the furminator.
They sell the real thing on ebay for pretty cheap...so check there before you pay retail
I have a "bamboo" hair removal tool...looks like a red/white half-circle with a blade sticking out of it. At $9, I figured I'd try it to see if it worked (and not spend over twice that on a furminator). It seems to work very well, although I can't compare to the furminator since I don't own one.
I got it at petsmart, so I assume it is readily available.
I have never tried the knock off furminator before but I have the real one and it works wonder. It's amazing how much fur I can get off from my short hair cats. I could make a mini pillow from the furs I get off of them. They even like to use it to brush against their face. I'm very careful about that because I don't know whether it will hurt them but they seem to love it!
It's hard to say because like the others who have answered, I haven't used a knock off brand. I bought my furminator from someone who had one and didn't care for it (I think I paid $10). I love it and Peaches responds to it better then when I try to comb her. I still comb her too... I just get less negative reaction with the furminator!