The big pic is of the 7100, look at the small pic for the FX.
Louise, I test rode a 7.3FX 2008 among others for my new commuter, at £350 with V-brakes, and really liked it. The one I rode had EF60 shifters which I thought looked tacky and let the bike down a bit, but they worked OK. On gravel / towpaths etc. I think the ally forks might feel a bit harsh through the handlebars, but I don't think it's a big issue. I think it is more of a tarmac bike though - the 7300 with front sus is more aimed at the bike path / gravel path.
If this really is a 2007 it's been knocking around a while, but that's a pretty good price for what I thought was a very nice, and pretty quick, bike, and had I been offered a 20" at that price I think I'd have snapped it up. A second-hand 2008 7.3 with V-brakes has just sold at £265 on
eBay.
If you do have the opportunity to ride one I would, though - the 2008 / 2009 aren't that different so you could try one of those. 15" sounds very small, but maybe you are!