. . . between worthy competitors, and let there be no doubt that the Brequet XX and XXI, as well as the IWC 5001, are essentially comparable designs.
All three lean more towards formality and appearance than casualness and utility. These are chronographs that are meant to be seen and not worked, rather like the distinction between a show and a work horse.
The G O has the benefit of a manufacture base movement, but equipped with an outsourced module for the chronograph. This may or may not be a factor in your assessment - only you can decide on that count. The base cal 39 automatic movement is one that I have some experience with, and I can say with a measure of certainty that it's a rugged, durable movement with a high level of finish, and capable of excellent performance when properly dialed in. My one cal 39 chronograph was an outstanding performer, and pretty much sealed my affection for the Manufacturer.
So long as you're comfortable accepting the G O on its own terms, this watch offers a level of finish and attention to detail that will retain your interest once the novelty has worn off. Tony A has one, and perhaps he'll add his words of wisdom for our benefit.
Cordially, Art.