I have a Pool Rover Plus. I bought it for exactly the reason you said, I was worried about it damaging the vinyl liner. Right now I use it in conjunction with a Pool Buster. Pretty good combo! (search the forums, you will find extensive opinions on both). Here is my take after a full season with the Rover (which we have nicknamed "Rover"):

PROS - It does an excellent job at vacuuming the pool, pulls in more stuff than you can believe. BUT, you cannot watch it - it will drive you crazy because it seems to go over the same spot again and again - but if you go away and come back 2 hours later, the pool is clean. Works well with large leaf loads too. Doesn't touch the vinyl. Doesn't get hung up on stairs or main drain covers. Does a GREAT job with blown in dirt and sand with the fine bag. It is FAST, one or 2 hours for my 20x40 pool (I will run it twice to pick up big leaf loads sometimes). Doesn't do vertical walls, but DOES climb up the side slopes on the deep end. Cheaper - I got my for about $600 new on the web at an authorized dealer.

CONS - Doesn't do the deep end corners well at all, leaves little pile of dirt/sand there. Doesn't climb to the water line. Cord tends to get tangled up, especially if you run it twice without switching the turn direction. The biggest thing is the lack of scrubbing. I find that I have to brush my pool every week or so to get rid of slickness, even though I keep my chlorine correct.

I'm not 100% sure I would buy the Rover again IF I knew that an Aquabot would do a better job AND not have more problems (such as damaging the liner). I would love to have both and run side by side tests in my pool, but don't have that option! Thats my 2 cents!