I used one many years ago -- It was fine - I placed mine in a sheltered spot in my garden mainly to protect it from the wind – I never heated it but used it just a huge cloche really to protect plants from the frost – I did have some success with tomatoes in it – But you must remember it has its limitation. _ Ken

You need to make sure it is out of the wind and put some heavy slabs in the bottom to anchor it down. My friend has fixed one somehow to the side of her shed.

I have always been happy with mine,as I haven't room for a greenhouse either..but as said above,it needs weighting down, If you are putting your pots in it,that should be ok..I store some pots over winter on the bottom shelf,for extra stability,and it is also secured to a waist high fence..I would advise you to get a decent make,as some of the cheaper ones haven't got removable shelves,and they tend to bow with the weight..If you decide at some point to grow tomato's or runner beans,it's ideal to be able to remove the shelving.and you can still use the outer cover till they get too tall....by then there will be no risk of frost....she says optimistically..:o).I do have a cheaper one as well,but I only use it as staging in the Conservatory,for overwintering tender plants,and for cuttings..hope this helps..

Thanks everyone - looking again at them and think maybe I'll make a coldframe out of twinwall instead. I have visions of the whole thing toppling over with the weight of my plant pots and would rather leave pots at ground level.
I want something that can be collapsed and put away once the weather warms up - it's just to protect things from the worst of the cold/snow/rain over the winter. Certainly not intending to grow anything edible when there are perfectly good farmers doing that for me.