Any time I've bought something in a Halfords it's pretty much always turned out to be a false economy. I'd rather just go to a decent LBS, where at least they know what they're talking about. At Halfords a lot of the employees only seem to know about go faster stripes, which radio has the best bass and how to lower suspension.
Of course, that could just be the ones I've been in! And I'm sure I'm maligning some of the employees, too.