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Virtually any model can be put on a leather strap so no issues with model there. You need to try these models on, there is a huge difference in size between a Super Avenger (I assume that's the one you mean) and a Montbrillant. Maintenance will be the same - service every 5 - 7 years as with any mechanical watch, and assuming that you aren't talking about the in house Montbrillant 01 the costs will be equivalent (in house would be more). Other than that it's personal taste and lifestyle - the Montbrillant has virtually no water resistance so isn't going to be practical for any activities where it may get wet.

Pilots wear most any model I am sure, but the Navitimer range (including Montbrillant) were designed as pilot's watches. 30 metres / 3 atmospheres water resistance (which is static water pressure and therefore much less in the real world) is fine for rain, but you shouldn't shower with it on or expose it to the full pressure of a domestic tap / faucet.

The Montbrilliant and other Navitimer line models are probably the most unmistakably Breitling pieces. I apologize if I sound too simplistic with the following, but I'm taking you at your word that you don't know Breitlings. One reason they became known as pilots watches was because of their functionality, specifically the ability to use the pieces to make manual flight-specific calculations. All those numbers on the outer ring are a circular slide rule, used by rotating the knurled bezel, or outer edge of the watch case. Breitling provides a "how to use" guide with each one they sell. You can also do simple math calculations, as with any slide rule, though I doubt many of us who own one actually do-- it's just a beautiful and uniquely styled watch.