I had a couple of the Four Tier Wide ones (can't remember the make, Halls maybe?
) but I bought them from Focus, and they lasted well through a whole season (tied to a hedge for stability) before the covers started to come apart. The shelving is now being used as staging in the greenhouse, and I've bought another one this year.
The narrower 4 tier ones I've bought in the past (Gardman I think) haven't been so good, even with a blob of silicone in all the joints when assembling (which I do in all of them) they still seem to fall to pieces remarkably easily, & the covers are flimsy at best.
I had a Growbag Cover thingy one year, the cover wasn't too bad, but the frame was wobbly
Get the silicone out if you buy one!