I posted about these before. I didn't think they would work either. Just for fun I went and test-drove one.
I have no connections to Altoz, but the tracked ones are the smoothest zero-turns I have ever used. And the videos are true -- they don't slip on wet side slopes and you can go through wet ditches just like they show. For the short amount of trial I did on a finished lawn (about 2 acres fescue) it didn't tear up the sod like I thought it would. Sure if you do a true tank-style pivot steer (1 lever forward and 1 backward) you will tear up the lawn but if you turn "gradually" it actually performed very well (as somebody above said, similar to wheeled vs. tracked skid-steer).
I didn't end up buying one because the price was higher than I could justify for my flat, finished lawn. But they are definitely worth a look if you have side slopes or low, wet areas that you need to mow on a regular basis.