I used Glasses Direct aswell. Got tested at the optician, filled in the details online, and got a pair for £160 as opposed to £450 from the optician (better lenses aswell). They queried the pupil measurement I supplied, so I sent off an old pair of glasses (they supplied the postage label and packing).
Still using the same pair three years later, my previous pair from the optician lasted two years. About to get tested again to see if my prescription has changed, but would definitely recommend Glasses Direct.