Have experience of two, my mumís and a mates.
My mum bought one of the early ones (about 10 years ago), and when it worked, it was brilliant. The grass was cut every night, no problems. But the fault rate was pretty terrible - lots of repairs and it ate lead-acid batteries, needing a new set every year. Tracing faults in the limiting wire was a complete pain. She got rid of it last year, it became cheaper and more reliable to pay the neighbours teenager a tenner to cut the grass with a normal mower.
A mate bought a top end Husqvarna last year. 2 cutters, li-ion batteries, itís a beast. Itís also spent more time in the workshop than actually cutting grass.
It seems like a brilliant idea that really should work, but the implementation isnít quite there. I suspect complex electronics + water + grass + the usual knocks that happen in a garden is not a great combination.