I used to use seed starter trays with lots of little pockets, but the pocket trays always got damaged and I felt that they made the sprouts root bound - so this is my 'ALTERNATIVE'.
I still use the top and bottom of the tray(s) as a convenient water tight tray - and also to hold moisture in at first when the seeds first sprout up. What you are about to see is what I do after the sprouts begin to form their second pair of leaves.
The tray that you see the "CUPS" in is actually the clear top cover of the seed sprouting set, you can use either one or both. All that matters is that you have something that holds water so that you can either put water in the tray to let it "Flow UP" into the seed cups, or so that the cups/pots can drain without a mess.
Chances are you might plant seed close enough together that you WILL need to use both the top and the bottom halves to set them in cups. I found three rows of nine or ten was about right to plant in the open tray, this means you have right about thirty sprouts, and you can fit up to eighteen cups in the trays with six to a row (but it's rather tight).
Some other things about using cups like this are that the shape of the cups makes it very easy to get the plants out of the cups when it is time to. That was another thing that bothered me about the pocket inserts - these cups are hassle-free.
They are also very durable, once you drill them and use them, you can stack them and put them away for later use even if they have been outside in full sun for a while.
Another note is that you really can't beat the price and availability. I have seen pots that size for as much as a dollar to a dollar and half each, and I decided THAT was nuts...
The hole size in the bottom (don't know if you noticed it - it was just under the first "O" in SOLO) can be quite small. It only needs to be large enough to let water in and out, and hopefully not dirt/soil/potting mix.
Just don't leave a clean one where somebody might fill it with a drink and have it dribble down their shirt - it's happened before, and is a practical joke that is definately not appreciated if it leaves a permanent stain...