that label doesn't look like a model m to me
The UK (greenrock) labels look different than the USA (lexington ?) ones. That label is missing half of it (not too uncommon on greenrock ones, I think they used worse glue) but the bottom half looks like it should.
$51 is probably a good deal for a UK model M. They aren't much cheaper in the states, and we all know how much harder it is to get one in the UK. There should be a beige label under that function-key-sticker on the case, judging by the detachable SDL cable. I recommend testing it before buying if possible.
Note: I don't follow pricing on the UK eBay, you may want to check with a UK member to make sure. Looks to be pretty clean and is only missing one relatively unimportant keycap.