Just started using my M80 yesterday to take my precious AVRI Precision to the bass doctor for a checkup and adjustment. Now I see why people love 'em. Rigid enough to protect the neck, and has that cool Headlock thing. Light enough to perish any thought of transporting a bass in a hard case in most circumstances. Ahem, most circumstances.
Now...airlines are another matter. Tough dilemma there. Last time I flew American from LAX, there was a gigantic and very mean-looking dude literally throwing suitcases in the air to load the conveyor. :scowl: That guy is the enemy.
If you put the bass in a $300 anti-Neanderthal flight case, they will probably make you check it and charge you the big bucks. If it's in a gig bag, they might let you carry it on. The M80 is sort of in between so it wouldn't be a disaster either way. But if forced to choose, I think I would leave the M80 safe at home and use one of the those semi-rigid Gator cases instead. I'd try to charm the gate agent and carry it on. Worst case, gate check, less trauma.