Not particularly good though. I did a fair bit of looking at them and tried a few on loan a couple years ago. At the time at least, you have to set up an electronic fence to set boundaries, which is very annoying if you have scattered garden beds or other obstacles it cannot bump into.

Also like Roombas (the brand, not robot vacuums in general) they have poor sensors and no real coverages algorithms, they just semi randomly roam around.

Battery life is also terrible, outdoor charging stations are harder to maintain etc.

All I’m saying is, there is a long way to go before they become defacto better than a person with a mower, they are a fair bit of work and fuss right now to set up and keep running.