Hello, I am new to this forum. We have a small allotment (more queries with that later!), and we are going to trial no-dig gardening having read Charles’ book from cover to cover. On the subject of module trays, I use ones from a local nursery that ‘grow on’ plug plants. They get their plugs in them, and they vary in plug size from really tiny to about 5cm across. There are about 84 cells to each one.They are stacked in a huge pile at the back of one of the glasshouses and customers help themselves! They are very rigid and sturdy and I think they will last for years. They have a hole in the bottom of each cell that I cover with a little square of card before adding compost. This can easily be pushed out at planting time.
I suggest if you have a similar nursery near you to try them.
Am eagerly awaiting new book, could do with it now!