Having had the pleasure of trying it (see here: http://www.watchprosite.com/montblanc/-span-style-color-gray--montblanc--span-sihh-2017-the-timewalker-for-purists--montblanc-s-timewalker-rally-timer/1006.1106853.8309113/0/ for some impressions) I can say it definitely wears smaller than the 50mm case size would suggest.
The dial design does follow vintage Minerva Rally Timers, too and having minutes instead of hours denoted at hour markers is fit for purpose.
While having it a bit smaller would be easier for wrist wear, the legibility would be compromised for the other applications and I guess a rotating case / support for table applications would be hard to engineer for a smaller case size.
And as this is unlikely to be the only watch in anyone's collection...