They're fantastic, the 45mm diameter cell is sufficient to cater for most seeds right up to the "planting out" stage. Compact little roots are formed, making transplanting simple with nearly no stress at all to the plants.
However we do recommend "planting out" before the roots become overgrown and start growing "in circles" within the cell! Made of lightweight PVC making it easy to "pop" the plants out when ready.
Tray dimensions are 505mm x 305mm x 50mm.