has no date, which IMHO looks so much better. They both have the Caliber 582 and the XXI has a 24 hour display. There is a price difference of Euro 2000.- Great watch. Geo
The Type XX has a traditional chronograph layout with the minutes counter at 3 o'clock, hour counter at 6 o'clock, central chronograph seconds hand and sub-second hand at 9 o'clock. The Type XXI has a central chronograph seconds hand AND a central chronographs minutes counter, with a 24 hour hand at 3 o'clock, an hour counter at 6 o'clock and sub -seconds at 3. This does giive it a more complicated look.
The Type XXI also have a more highly elaborated dial, that some find very pleasing but some may find a bit overwrought. If has more steps and subtle colors and little indices in addition to luminous markings, etc. I don't like it nearly as much as the Type XX personally, but I also favor the smaller size as well.
While I also prefer the cleaner look and smaller size of the Type XX, I found the chronograph difficult to read. I found that the two-minute increments in the minute chronograph totalizer makes it difficult (to me) to read elapsed time quickly at a glance. Perhaps I'm in the minority, but it is a factor to consider if you plan to actually use the chronograph feature on that beautiful watch.