Yamaha DTXpress/DTXplorer/DTXtreme

Hey guys great group and i have been scanning the messages for a few 
weeks now. As an interested e-drummer, whose interest lies 
specifically in the variety of sounds and the ability to practice in 
a quieter environment than my currrent acoustic kit, I have arranged 
to go look at a guy who is moving to the US(from the UK) Yamaha 
DTXPRESS 2 kit. I was just wondering what kind of things i should 
check out and ensure to ask him before committing to buying the kit 
off him.