This is my first year growing in Earthboxes and I kept my regular gardens as well.
The concept is that the box has a water reservoir that wicks up through a high quality potting mix and fertilizer, ensuring that the plants can't be over or under watered. The cover keeps weeds out and moisture in. The pipe in the corner is used to fill the reservoir and the indent in the bottom is the overflow slot. When water dribbles out there I know the box has enough.
This box holds three bell peppers with a pea fence around for extra support.
Now that the gardening season is well advanced I can offer some opinions. The only things that didn't thrive were the peas. It's best to plant seedlings instead of seeds which limits the usefulness to plants that can be transplanted. Lettuce and broccoli grew like crazy and drank a lot of water every day. Overall, I'm very happy with the performance and look forward to trying different crops next year.