hi Thomas, I came across these online just today. I am wanting to reduce my plastic consumption, so hence my search. These are, however, extremely expensive at 73€ each for the wide tray; they should last a long time though!
I have also been looking for something more robust than those generally available. I have just received some propagation trays (8×5 modules per tray) from containerwise.co.uk. These are fully rigid and should last many years. The website appears to be for the wholesale market wanting large quantities but they will sell to individuals: I got 10 trays for £54.59 (incl VAT and p&p). Charles uses these in his latest video.