My thoughts:
I had an Evoluent Vertical Mouse 3 that I sold to Ironman31. I really liked it as opposed to a conventional mouse, the vertical part is good, plenty of buttons, feels great, etc, but I am so spoiled by the Rollermouse...so why slide my hand/arm all over the desk with a mouse? This ain't the stone age. But, let me be clear, I found nothing wrong with the Evoluent and recommend it.
I have used the Rollermouse with my Kinesis for years. It is not a perfect match only because of the obvious height difference which takes away a bit of the ergo and the convenience, but consider this....
1) The RollerMouse is a very highly awesome pointing device at several levels (ergo, features, benefits, etc.)
2 I love the Kinesis Advantage and can't/won't type on many other things. (only other keyboards I like to use are Datahand and Alphagrip)
3) At this point, I am a bit biased towards the RollerMouse (because it's the ****!). So it's worth the less-than-full-benefit of the ergo and convenience to use it in conjunction with the Kinesis Advantage, (which I am also hooked on).
I can't stress enough that the Rollermouse should be tried. Watching a youtube video just doesn't convey how it works. Contour Designs offers a 30 day free trial, that's how confident they are. About 5 people that have stayed with me when on vacation (I live at the beach in California) have gone back home to their lives in the snow, but treated themselves to their own Rollermouse. That'r a pretty big statement for the Rollermouse.
Jpc is so correct in using keyboard shortcuts. If you can remember them, they are by far the most effective method of control, and you should try to reduce any pointing device usage if you have RSI.
I hope my honest disclaimer (I love Kinesis Advantage, I love RollerMouse) helps balance my genuine enthusiasm for the great product that the Rollermouse is.