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It's the late 2011" - what do you think?That's either the Early 2011 or the Late 2011 model. If the Radeon graphics card has 512 MB RAM, then it's the Late 2011 model. If it has 1 GB RAM, then it's the Early 2011 model.
In any case, if I feed the specs into Mac2sell.net then they estimate a £660 value. In this case, it's boxed and you get warranty as well.
I think it's pretty decent. It's not a bargain, it's a decent price. Note however, that if you want a nice performant machine, you need to install an SSD. That's going to cost about another 60 quid if you can install it yourself.