I would also be interested to find out how they are. In my case I am thinking of adding them to an existing system to increase heating surface and reduce Δt in my heating system.
I installed Thermaskirt in an extension that was added to my property in 2014. The extension created an open plan, triple aspect, lounge/dining/kitchen of ~41 sq.m. I wanted to minimise radiators so that wall space was available for furniture. I ended up with 16.4m of Thermaskirt and two radiators to get the heat output I calculated was needed for the room. It’s worked well with no problems.