Hmmm, that's weird - one of mine is at least 8 years old and still looks good.. As I say, I chose mine for aesthetic reasons because I like the clear look. I still have all the twinwall panels and toyed with the idea of building a lean to style with the panels but decided if I didn't like the look in a greenhouse what would make me like it any better as a lean to.
....
Just went and looked at my warranty. The entire greenhouse is warranted for only 5 years but I have yet to see signs of any failure. Panels are lovely and clear, frame is sturdy. Guess it's like the 3 year warranty on a fridge, you know that it's not going to die in that time frame it is just limiting the manufacturers liability- a good move!
I also chose mine because I had to assemble them myself. No extra pairs of hands to help and these are doable for one person
Lots of variables to sway a person's choice.
As I said before, it is an individual choice. All three of my greenhouses are in view from my kitchen and I went with the clear look because it is a personal preference.