Use an egg carton to start seeds?

While cooking for T-day, I realized that the foam egg cartons I was throwing away would make nice germination trays for some euphorbia seeds I need to start. Holes can be poked, some C&S mix put into each spot, and the cartons can be cut to fit under a soda bottle humidity dome. The whole set-up fits on my heat mat. Has anyone else used a egg carton for seed germination? Is there something I'm missing? I've not germinated seeds before, these will be my first and I don't want to lose my euphorbia seedlings before I start.

I haven't used the styrofoam egg cartons but I have used the cardboard egg cartons. Those were very nice (and cheap) because I was able to just cut them apart with a scissors and plant them straight in the ground without disturbing the seedling.

I've used the egg cartons (styro) to grow seeds during the winter. Once the seedlings were pretty big I would transplant to a larger pot and then a larger. I have also put these pellets that u soak and they expand and u put the seeds in an opening on top. That made it easier to transplant as they roots were undisturbed. I had everyone in the family bringing me cartons and now Im set for a couple of life times.......

I also have used the individual serving size of puddings and jello that are sold in the dairy case.
Since I have found the Jello I buy pretty much of it as it is so handy and good for strong fingernails and hair.
Poke some holes into the bottom of the styro also to give the water someplace to drain to.

I've used the egg cartons, both cardboard and styro. I use the lid of the carton as a tray underneath the bottom to collect any drippage (usually only works with the stryro though).