I got this a while back, and haven't noticed any lag with it. Cost me $7 including shipping ^_^. I'll try the USB rate tweaker eventually and see if i notice a difference though.
If you don't wanna go to the ebay page, it looks like this:
As an added note to anyone looking to get one of these, make sure you do NOT get the 4-player version. For some reason it seems like the four-player version cycles between reading each port, even if there's nothing plugged in, so what ends up happening is you get dropped inputs like crazy. It works great for everything that's not a fighting game, such as emulators, but it is god-awful for any fighting game.
Maybe the USB rate tweaker would help a little, but I'd rather just get something like the Pelican or EMS2. So far the EMS2 is the best one I've used, and I've never even considered using a rate tweaker with it. It's something to look into.