Hi there. Those coldframes are great in all sorts of ways. They let in uvb and the design of them is brilliant but they were expensive and v. difficult to get hold of.
I've now got 2 other uvb transmitting coldframes too which were much cheaper. The Jewel Paula comes in at £200. It's easy to assemble. Designed for tortoises and has a sliding roof with a mesh underneath. So the roof can be open to the air in good weather but the torts can't be attacked by birds.
https://www.bluelizardreptiles.co.uk.../9001567201467
It says in the blurb there that the cold frame is made of polycarbonate which is selling it short. It's made of Alltop which is uvb transmitting and has two walls so like double glazing. Great for keeping heat in.
I'd say the Paula is well worth looking at for anyone getting a coldframe for a tortoise.