I would greatly recommend the II over the E if you're using it in your Prius. The E doesn't support X-gauges, which is one of the main reasons I would get a Scangauge over an Ultragauge.
Thanks for the advice! Wasn't sure about differences. I figured the 2 would be better but didn't know.
E is a newer, lower cost version. It only shows 2 gauges at a time instead of 4. Its fine if you want a simple gauge in a regular gas car, but in a hybrid, you'll want the extra goodies the X-gauges can show.