I can't speak for the TeraHydro design, but I have 5 years experience with my EarthTainer design, and from this I recommend 2 full sized tomato plants per 'Tainer maximum. In my view, it is all about the cubic area which you give the plant to grow in, on a relative basis. Yes, with certain hydroponic systems you can get higher densities but the nutrient requirements escalate accordingly.
This Season I crammed 5 Pepper plants into each EarthTainer and this was a big mistake. While lots of foliage and numerous fruit, the Peppers were small. Next Season I am going to plant only 2 Pepper plants per 'Tainer and give each of the plants room to fully develop.
Raybo