Bought my parents one a few years ago (fitted myself) as they’re both having trouble getting in and out of their cars so it saves them the effort. The old door was knackered and it was only an extra £150 on top of what they were going to spend anyway!
Things I remember is to make sure the frame is straight and level and to, if possible, a separate supply for the motor. My parent’s frame is slightly off-level by 4 degrees so the door doesn’t come down as cleanly as it should, sometimes rattles as it slides down. I’ve put nylon sheets inside the runners to help but it still can be noisy occasionally. To get the frame level would be a massive job, wall down, roof lifted etc, so they just live with the odd rattle. They very rarely go out at night so the neighbours don’t mind it at all. Two of them can’t complain as theirs (bought after us) do the same thing! I think the whole street must be tilted!
Cost was £550 delivered for a security style one that is powder-coated to blend in. Looks a lot more expensive and just needs the occasional wipe down with a sponge to come up as new.