I spent about 30 minutes reviewing and experimenting with the applets available. Most of the simulations model concepts that I would like to show my students. I wish I had the ones dealing with angles inside circles about a month ago. I would have used them in my lessons.
I think that these would be best used as a demonstration to spark conversation about concepts. They are not something that my students would use for long periods of time. They are just simple simulations to explore a concept and develop a conclusion.
The applets are very simple and easy to use. For most of them you just click and drag vertices where you want them.