http://www.rail-reg.gov.uk/server/show/nav.1559
It's nothing more than a Fluke 287 which has been tested and approved for use on these systems.
So it would be fine on hobby electronics, I found out it was used on railway engineering.
Yes, it's just a multimeter.
A little more digging shows Fluke 115, 117, 179, and 87V models are also available as TPWS approved, and there's one on ebay (I assume the one you're looking at) which looks like a 187. They're nothing special, just red tape.
E: And clamp meters, IR thermometers, thermal imaging cameras, insulation testers, and power analyzers. Fluke are making a pretty penny here.