They seem to be pretty reliable. Most of their products are cool, some can void the warranty, none are likely to screw up your car. As far as I know, none of their products affect or require messing with the high voltage parts of the Prius. Still, you should maintain a healthy respect for them when doing any installation or other work on your Prius.
By voiding the warranty, I mean that if installation or use of these accessories causes a failure of some part(s) of your Prius, it won't be covered by the warranty. Failures of parts not involved in installation or use of the accessories will still be covered to the same extent they would had you not installed/used the accessories. This is pretty much standard for the automotive after market industry.