It's not the knees which are the problem, a few wrong landings bugger the shoulders and wrists pretty quickly though. I rode biketrials for many years and fully rigid bikes tend to be unforgiving, but are really what you need. I can't imagine that road bike lasting too long though given how much hardcore mtb and trials specific stuff gets broken in the sport. It's fun though and will perk up your balance and slow speed handling big time.
still, impressive to see it done on a road bike.
tony