We are both big fans of Charles Dowding's 'no dig' approach to gardening and have both enjoyed Charles' courses at Homeacres. So we were thrilled when Charles agreed to try out our natural rubber seed tray. (Ours is the tray on the right of the photo). Charles said the following: 

'Great result, lovely plants, easy to use. I like the small cells. 

I thought she small drainage holes might be a problem, especially by making it more difficult to push the rootball up when planting. However because the tray is so flexible, plants push up easily and the rootball is not damaged.

Drainage is fine, growth is steady.

On size I would not go smaller. The size you have is ideal for starting almost all veg and few modules can offer that. The amount of compost used is not excessive, space requirement is fine, say germinating on a windowsill.'