The gentle and symmetrical row angles of the prototype(s) remind me of SA, which has some minor benefits, but I know the community likes row profiles that are more Cherry/Beamspring-ish. And the roundness of MT3 makes them superior, shape-wise, to any other spherical keycap being made today, so that's something to think about.
I do like the depth of dishing and the smoothness of the gradient from the top ridge to the center of the keycap in the prototype(s). Topre Hi-Pro keycaps have too sharp a ridge crease for my tastes, and MT3 comes dangerously close to that as well, but is a bit better than Hi-Pros in that regard. SA has the gentlest gradient of all, but they aren't dished deeply enough, IMO. In fact, I think that the deep-dish mold for SA should be the standard mold for SA, and they should make their deep dish keys a bit deeper still. That's why I like the dishing in the prototype(s); they seem to strike just the right balance, though I'd like to see what a deep dish prototype would look like as well.
Personally I don't care for the huge drop-off that Topre's Hi-Pro keycaps have, both from the numrow to the F-row, and from the Shift-row to the bottom row. It is neither aesthetically pleasing nor ergonomic. I have a Topre 104UK Hi-Pro and those drop-offs are rather unpleasant, to be frank.