The sizzix is pretty much universal when it comes to dies.. You can use cuttlebug, spellbinders, quickuts, etc... Just think about what you want to make...
The most important thing to know is make sure you get the good felt.. By that, I mean wool or wool blend felt. Quality felt means you are going to get a quality cut when you run it through the machine.
I have bought a lot of craft felt, like at joann's, on the bolt & in the felt aisle.. Unless you are using it to cut out simple circles to put on the back of your clips, I wouldn't use it (IMO)...
So, back to dies. I think the sizzix bigz dies work the best when cutting. I can add up to 6 or 7 layers of my felt & cut & they are perfect!
Cuttlebug & spellbinders, you will have to use the multipurpose platform thing, but they will work.
Okay. So hopefully this book of mine made sense. I just got done cleaning up a basement full of water, so my brain is a bit loopy