I made one of these self-watering barrels about 6 years ago. They work great. I've raised cantaloupe, gourds, cherry tomatoes with success. They work just like an Earthbox, but only on a giant scale. It can grow about 4 times what fits one Earthbox and I use 4 times the lime and fertilizer each year.
Instead of cutting the barrel in half like the instructable says, I used full-size barrels. The soil/water division shelf is about 2/3 soil and 1/3 water. I used a five-gallon bucket with holes drilled in it as the "soil shelf" and "soil water wick". A water drainage hole in the barrel leaves and air space between the soil and the water level to keep it from getting water-logged. I used a piece of lattice trellis to lead the vine plants from the barrel to the ground and to support the produce. I'll post a photo of my set-up to compare to the instructable.
Now that I'm 70 years old, I wish all my plants were "chest high" like the barrel. This year, it will contain 4 cantaloupe and two cherry tomatoes. I normalyl use a plastic cover on it, but this year, I think I'lll just put some mulch on top once the plants are more established.
If one is good, three is better. I'm posting this to show how I used plastic lattice as plant support. I used plastic zip-ties to make a circle of each lattice. It's plenty strong enough to support cantaloupes, etc. In the photo, I forgot to lay plastic under the lattice. I didn't make that mistake this year. Weeds will go through the lattice holes if nothing prevents that.