What's the catch?

That laptop's fairly tidy , what you have found there is someone selling off last generations old third gen I5 chip , intel released the 4th gen mobile chip-sets very this quarter ( IE Aug-September ) So there will be some stock sell off on the older generation I5 ..... this does not mean that is is a bad purchase .... the newer i5's are less power hungry , but not a whole lot more bang for buck.

That looks like a pretty tidy machine .... HOWEVER the same seller actually has an I7
Toshiba S50-10V with the same nvidia 740 .... for the same price .

Normally for games i don't rate the i7 on desktops but on a laptop its a different chip entirely.

The downside is a smaller screen , which is my eyes is a benefit .... speaking as a comp science graduate who used to lug a heavy machine in and out ever day .... get a second larger screen and connect it to the laptop for use in your digs , and you can use that as a TV replacement as well , If for some reason the machine struggles to push both displays you can close the laptop lid and run it just as on the standalone monitor. a nice 22 inch panel will run you under 100 quid. and can even be bought way later

best of luck