It is an amazing controller. Bar none the best controller of that form factor in the mobile space. The trigger and button feel make the upgrades done on the Switch Lite feel halfway done. The grips themselves are ergonomic enough without adding bulk: especially compared to the Kishi. The audio and battery ports are well located and have a good snug fit.
The community building aspect of the backbone is interesting but there needs to be a “remote play/steaming gamer” option where one of the two backbone buttons (either recording or software launch) becomes a HOME button. It is a real inconvenience not to have this button when using Steam, PS Remote Play and other services that leverage a Home button for a large amount of use. If I am playing with the steam/Xbox/ps5 community I need access to that, not Backbone’s additional feature set. So this is actually a huge negative to an otherwise great piece of hardware.
The dpad is the only object of improvement on the hardware but software adjustment for a HOME button would make the A- hardware into A+ hardware.
My favorite controller is the Astro C40 so if they do a revision the Backbone Pro only needs a Home button and 2 small (removable?) paddles near the cross bar connections. That would be a slice of heaven. Xbox elite to Switch PowerA controller users are very used to paddles.