If it's well set up it would be a great rally outfit. Top speed would probably be limited to 60mph for comfort, but fuel wouldn't be too bad (late 40s, early 50s?).
I think it's a Velorex chair but I'm not sure it's a Velorex chassis. Looks neat enough, although it would be good to see some pictures of the fittings.
The biggest problem is getting an engine. Gareth had all sorts of trouble with his. You'd have to budget £300 at least for a motor (unless it's an easy fix).
The wheel conversion looks nice though eh?
A chair already fitted is (generally) a whole lot less hassle than fitting one from scratch, but careful ebaying can snag you a bike, a chair and fittings for buttons. Gareth's ER5 outfit cost him just over £800 in total (although it took some time and fabrication to get it all to mate up).
GC