From the supplier- “23mm thick uniquely backed with galvanised steel and offer superb clarity that cannot be matched by any other mirror supplier as our system is unique to us, and can be adapted to both outdoor and indoor, Vertical and Horizontal installation configurations. Following the installation of the mirrors your schooling will be twice as effective as you will be able to assess the straightness outline and quality of movement visually.”

I have had them as one vertical and 3 horizontal and mounted them myself in my indoor arena. They have been on my trailer and covered with a tarpaulin for 2 years however, but zero cracks, knocks, marks or issues.

£250 each mirror or £900ono for all 4, would prefer to sell all 4 together. (Currently selling new for double this.)
I can deliver within reasonable distance of fordingbridge or happy to assist and deliver further afield for fuel/time costs.