N,
I've been using Dolphin Robots for about 15 years or so..
I bought two used Dolphin Diagnostics that I fixed up and ran for about 6 or 7 years in rent house pools.. When I built my pool I bought a Dolphin Premier that just gave up the ghost a few weeks ago which made it about 7 years old. Over the past couple of years I have replaced them all with Dolphin S200 (style) robots.. They are twice the cleaner the Premier was at about half the cost.. I won't know about the reliability of the new units for a few more years..
My gut says that the average life of a robot is about 5 years.
My Premier was expensive, came with a caddy and remote. I used the remote once and that was the day I got it. I found the caddy, for me, was useless... I keep my robots near the pool and mount the power supply to a wall.. I have zero need for the fancy bells and whistles that just make the robot cost more, but do not make it clean any better..
As far as the leave-it-in-the-pool, or take-it-out-each-day, question... I do both.. I don't like to see it in my pool, so it normally gets removed when done cleaning.. But the two units at my rent houses, just live in the pool unless the tenant takes it out..
Thanks,
Jim R.