I have purchased a number of these trays and find them to be strong, durable, and do not break down from sunlight. I presently use them to place my smaller pots and transplants into for a multitude of reasons such as watering and movement. With some of my larger pots, i fill the trays with water, set the pots inside and wait until the water is absorbed naturally. I do not usually start with seeds for the cactus and succulents due to the difficulty in germination. The vegetables and flowers do quite well using this combination of heating pad, tray, and the clear dome for germination and transplanting to small individual containers.
On the other hand, the plastic covers are thin, somewhat flimsy, but fit on top of the trays nicely. When starting some seeds this is a nice way to go. I also use a heating pad for a controlled environment inside the enclosed space. The only thing I complain about is that the condensation build-up on the inside of the dome sometimes leaks where the dome lid and the tray meet. Other than these thing, this is a great combination.