I'm gonna answer my own question just in case someone else does a search on this.
I bought a boostaroo revolution, set my mp3 player and car stereo volumes to a good setting, then played the same songs through both the revolution and the original. I couldn't hear any difference in the volume level from the revolution and the original, but I did hear more distortion/static from the revolution on certain songs. I expected the revolution to be a lot better than my radioshack brand boostaroo, but that wasn't the case at all. There are a couple of things going for the revolution, namely the small size and weight, but they are outweighed by what I think are major drawbacks: the battery door is next to impossible to open, it uses AAAA batteries and I can't use rechargeables, the volume wasn't any louder in my car, and it sometimes has more distortion. Hard to pay more than twice the cost of the original and still have all those drawbacks, IMO.