I use few of these because they tend to dry out. This is a concern since I leave the house during the day for work, and cannot leave seedlings in clay pots outdoors to harden off before planting. They will always require watering around mid- day. However, clay pots are reusable. Peppers were planted in these, but are not yet sprouted.
I have tried these a few times in the past, and never liked them. They sound like a great idea, but they can be on the expensive side and not work as they were intended. They dry out fast, too, needing constant watering. One year tomatoes were started in them and planted directly into the ground. The tomatoes were very slow growing, compared to those transplanted into bare earth. The peat pots did not disintegrate well into the soil as was expected. The roots seemed constricted and had trouble growing through the solid peat.
Plastic Yogurt Cups
With holes punched in the bottom, these wide-top cups are used every year and, work great. They are a perfect size, and we get some additional use from the plastic before it makes its way to the recycle bin. Since no one thinks of saving them throughout the winter, you end up eating a lot of yogurt just to get the cups in spring. Peppers were recently planted in these cups.
Plastic Seedling Flats
The 4 or 6 compartment black plastic cell inserts made for seedlings work well. However, the big box stores along with the gardening centers here only sell the prepackaged bundle consisting of cell inserts, clear plastic cover, and plastic flat watering tray. I only want and need the cell inserts, but unfortunately we are forced to purchase everything in the bundle. The cell inserts can be purchased online for pennies, but shipping costs kill the deal. Check out Home Harvest: 8 cells inserts cost $7.92; shipping costs $7.75.
These were tried one year and found to be too small. Soil also kept moving around from cell to cell. Seedlings were difficult to extract without damaging them.
Paper Dixie cups are my favorite. Tall shapes can be found to allow for root growth. They are paper and biodegradable. They can easily be broken apart without plant damage at transplanting time. They are cheap. The wax coating prevents drying out. Labeling with marker is difficult on the wax coating, though. Broccoli is sprouting in these in only five days.
My mom would cut off tops of milk cartons and had good luck starting seeds in the bottoms. Again, as with yogurt cups, one needs to save them.
Blooming: White forsythia
Seedlings progress: broccoli