Yep that arm and attachment looks an expensive bit of kit -- he even mentioned the website company that builds them. Impressive how some peoples determination allows them to conquer any obstacles they're faced (helped with modern day medicine and engineering). Definately impressive.
I was wondering if he races as well - as that video definately looked like a mx-track practice day.
We went to Geraint Jones enduro school last November and he was there, riding in our group. He never gave up, fixing his bike one handed after he flipped it and snapped off the rear mudguard, getting his gloves on using his teeth etc. He lost his arm in a road bike accident, hitting a motorway barrier. He had a group of mates with him, but there were no concessions to his armlessness. And he rode his bike well, and tried everything. An impressive individual.