That was a demo in a park, I dont own it but you can buy them from here.
Resistograph :: IML,Inc. Fujikura Europe | Speciality | Products | Decay Detection http://www.iml.de/
There's a 300mm version or 500mm version. One idea is that if trees are OK to 30% wall thickness then you dont need to drill much further than that 30%.
So a 300mm deep hole into a 2000mm (2m) dia tree would suffice.