Zipcode, this pic is what happened with my leek experiment. The three rows in the middle were potted up into individual cells, and this is how they look after some time in the field. On the sides, the ones from the mass planting can't catch up. Same thing happened with the onions, the ones from cells were bigger plants and in the end made bigger onions. I guess I should have done the same with shallots
It would definitely be worthwhile if you have the space.