I used a SmartPool Robo-Kleen cleaner for three years in my 15' intex donut. It stopped moving after three years. I liked it so well that I bought another last year when we had our 12x24 traditional AG installed. Both cost about $300 from local pool stores - seems to be a little less now on the Internet. 3 years doesn't seem like a long run but, for me, it paid for itself the very first time I used it. I did have it in the pool every day or every other day as our pool is surrounded by full grown pin oaks that drop stuff in the pool all year.
Two other advantages: 1) The filterbag is quite fine and fuzzy on the inside and catches alot of fine stuff. It significantly improved the water quality when I was using Intex cartridges - perhaps because it kept the particles in the water available to the filter. 2) It mixes the pool - I tried to be sure I added bleach etc. when the robot was working to be sure it wouldn't stay in one place long.
One other thing, the robo-kleen would occasionally "turtle" in the donut pool - sad robot laying on it's back unable to move. I found I could mitigate this by letting the cord have as many loops as it wants (the cord has a "lay" when it arrives) - more or less loops and the tendency for the cord to tangle itself increases and tangled cord leads to upside down robot.