I was able to put four Mini - I s in a T-Loc - III stacked flat. They fit in the T-Loc but not as nicely as in a Classic.
Five will fit on edge in a Classic Systainer - III, but not a T-Loc.
Checked out the catalog measurements and also did some measuring.
The T-Loc -I and Classic - I have the same overall height , but the lid thickness (including internal projections) of the T-Loc is about 5mm more than the Classic. That is enough to make the difference.
T- Loc - I and Classic - I = 105mm overall
T-Loc lid = about 40mm
Classic lid = about 35mm
Mini - I = 70mm overall
Mini - II = 87mm overall
-----------------------------------------------------------------------------------------------------------------------------
There is one difference between Tanos and Festool Systainers. On sizes II - IV, the Festool versions have a stiffener along the top back edge. Tanos do not. Neither have it on size - I. Both T-loc and Classic are like this.
Seth