I have 2 of the first ones they put out (Garden Tower 1); basically they were plastic barrels with pockets. These look like they will be much easier to use and better for growing.
One of the problems I ran into was that the legs splayed out afterb a few months of heavy watering so we had to put belts around the legs to keep them from breaking or the barrels from tilting over. You won't have that problem.
The worms didn't like being in there, they never actually took to it and so it kind of smelled while the compost was rotting. All the time in the hot weather.
I had to add more soil at the beginning just as you have said. But then later on the soil dried out in the top and middle pockets and shrank back even though the inside portion by the tube was still moist and the bottom pockets were well moistened. It was impossible to get the middle ones moistened again and I had to add soil every month or so. Hard to replant too, but it looks like your pockets might be bigger. I hesitate to use the water crystals, they never really work for me, either they make the top of the soil green or they dry out into little pebbles.
After they died, the roots of the plants were hard to get out too, especially sage and tomatoes growing in the pocket. Since it looks like yours comes apart, you have an solution to that, whether it will be easy or not remains to be seen.
I am not trying to make you not like these planters, I just wanted to point you at some things to watch for.
I'm not horribly disappointed with my barrels; I'm still using them in spite of the drawbacks. They do pretty good with herbs that can tolerate dryness and they do drain well.