Yup. Got 4 of them myself, plug in two PSX MAS sticks, works great. They are seriously the best things in the world. With Windows 2K/XP they're instantly recognized as 4 axis 16 button gamepads. Two things I've noticed:
The controller needs to be pushed in all the way into the adapter. This may sound stupid, but on one of mine if it is literall 2mm out it stops registering. I wrap rubber bands around it to hold it in place.
The other thing is if you have more than one plugged into your system, both have to have controllers connected to them. If I have both USB adapters plugged in, but only one controller connected to one of them, weird stuff starts happening.
That's it. If you get them you definately won't be disappointed.
P.S. If you're getting them from LevelSix: I've gotten 4 from them, they've all worked and were shipped immediately and came quickly. However, a friend of mine bought one that is broken, and unfortunately LevelSix has been totally unresponsive. He's sent multiple emails to support, sales, everything. Not a single reply. Just so you're warned.