I went through this same dilemma a year ago and got the U122. I fly United most of the time, and that fits their sizer perfectly, with no room to spare. But, I've never seen a GA use the sizer. (On a flight a couple of days ago, my seatmate brought a full-size guitar case on board. It fit the overhead bin, but took up a lot of space.)
I've used the case on quite a few European and Asian airlines with no problem, both business and economy. But it does exceed the dimensions for some airlines. The B&R bags are also heavy - some European airlines have tight weight limits, and the bag itself will use up more than half of your allowance.
If the airlines ever get really stringent about sizing bags at the gate, the only option will be to choose one small enough to comply with all or most, or own multiple bags for different itineraries.
The first carrier rule for US travelers means that the rules of the originating carrier apply. That was another factor in my choosing one for United sizer dimensions.
I've been happy with the B&R bag overall despite its weight. The compression feature is somewhat useful, and it tends to bulge less in the middle when stuffed compared to many roll-aboards. Looks like new after 130K miles.