What sort of greenhouse?

I am planning to get a greenhouse (my first, I feel like a proper gardener now!) but I am not sure whether I should be going for glass or polycarbonate.  I have small kids so safety is an issue but I also want the type that does the job best.  It's only going to be small, 6 x 4 and will be in a fairly sheltered spot.  Also it has to be cheapish (under £300).  Does anybody have any advice/recommendations?

I was looking at probably the same one but it looked really flimsy.  I wasn't sure whether that one was polycarbonate as I imagined the panels to be thicker than that.  They looked like the plastic pop bottles are made of.  (I may have been looking at a different one though).