Here is my opinion. The larger one is better. Don't bother with the 'mini' - they don't press together very well, they are very small (I guess the term mini should have been my clue), and it seems like they will dry out fast. The step up from the mini - the larger one pictured above - creates blocks that are just shy of 1.5" square with a little dimple in the top for the seed. I love this item!! I was able to make 110 blocks in no time flat this morning (not even an hour). They are easy to plant and water. (I had to replant my onions; the first batch of seeds were really old and I had tried them in the mini blocks, I wasn't happy - no sprouting and the little blocks were already falling apart.)
This morning I started 60 Australian Brown Onions, 20 Yellow of Parma Onions, 20 Blue Solaize Leeks, 5 Nutri-bud Broccoli, and 5 Long Island Brussels Sprouts. And another little tray of arugula.