What is the difference between the R-Go Waver and the R-Go Twister?

The Twister differs from the Waver in that it offers more features than the Waver. In particular, the Twister can be folded up for transport, whereas the Waver cannot. In this sense, the Waver is a simpler and more cost-effective model with (consequently) a wider range of applications. The Twister is an ambidextrous mouse designed primarily for a single, fixed user at various locations. The Waver is an ambidextrous mouse designed for simple and healthy use by multiple, alternating users at a single, fixed location. Of course, a Twister can also be used in exactly the same way as a Waver. And conversely, the Waver can also encourage you to switch between your dominant hand and the other! So it all depends on exactly HOW you wish to use the Waver.