The grow tray is where the plants sit, so choose one that drains well and fits your reservoir and pump.
Depth
The tray must be deep enough for the roots and the medium, but not so deep that it stays wet. Check the manufacturer’s guidance for your plants.
Drainage
A good tray drains completely through a drain hole or outlet. Make sure the drain is not blocked by medium or roots.
Fit and weight
A full tray is heavy. Make sure the stand and the reservoir can take the weight, and that the pump fits.