Interesting comments about the trays. I’m new here and very enthusiastic about getting going, although don’t think I need 4 trays yet. I certainly don’t want 60 of them! I did find some being sold individually on ebay so I will probably give it a go for trialling.
https://www.ebay.co.uk/itm/362541342859
It seems like the size of them may increase delivery charges too, so I’ll start with one and let you know how I get on.