Although the converter feels a bit heavy and ungainly, it's super easy to use. You just slide it right under the cutting area of the sizzix machine and the powerful magnet pulls it right into place. It doesn't shift out of place while you are cutting. It hangs in there easily and with no fuss. Popping it off is just as easy.
This converter makes it so I rarely use my sidekick anymore. I just pop the converter on and cut all of my sidekick dies in my original sizzix machine. I love it!
The only down side that I see is that sometimes I have to pump the Sizzix handle a bit more for the sizzlit dies than for the original dies (done without the converter, of course), but this doesn't really bother me. I still like the pump action handle better than trying to use the Sidekick and it works fine with 3 or so pumps of the handle. Definitely worth it.
I purchased this when I got my original big red machine. It allowed me to use Sizzix embossing templates... and also would theoretically allow me to someday use Sizzlits and dies from other manufacturers. I've done neither of those however. It is a little heavy - as has already been indicated - but I think it helps add to the pressure for even better die cutting once it is placed. And all one has to do to place it is just turn it correct side up and slide it until it is underneath metal plate on the Sizzix machine. The stong magnet in the converter will snap it right up into place. It won't come loose until you want it to.