I am myself very partial to the Glashutte Original Senator 100-based perpetual calendars, and often have recommended the steel version to friends as a perpetual calendar "best buy", but, unless I am mistaken, even its current Euro list price is nontrivially higher than the Montblanc. While I like window-based perpetuals enough better than their subdial-based cousins that I might still spring for the GO if I were making the choice, the Montblanc seems a really substantial value.