No doubt you could break your wrists when caught in barkbusters as that is the nature of freak accidents but I believe you can minimize the risk with proper set up of them.
Normally you would have your levers set slightly down at the front from level (approx15 degrees) so you can access the levers comfortably while standing.
Quite often the lever won’t fit inside the bark buster unless you use a shorty lever and even then it will be tight so if the lever won’t fit inside the bark busters then the busters should at least be slightly lower from level as well, not above the bars.
This will allow your hands to flow over the busters rather than through them in the case of a crash
I have seen a few bikes set up with the busters sitting higher than the bars which look to me like a recipe for disaster.
Side note; I remember a guy at a MX at Myrtleford in the 80’s broke both wrists when hitting a ditch in the track long before anyone was using barkbusters.