I have a M6R that I took on a flight with me recently.
I put it in a semi-rigid suitcase as mentioned in this post. The bike *just* fits if you struggle with the suitcase a bit. I had to remove the seatpost and saddle, and also the screws and clamps on the hinges to prevent them from sticking out too much. After first removing the seatpost the bike wanted to unfold itself, as it is the seatpost that locks the whole thing folded. So I just tied the wheels to the top tube when folded to keep the whole thing from unfolding.
I found it useful to wrap the whole bike in a big sheet of clear plastic, and then to put the whole thing in the suitcase - it's easier to handle that way, and it keeps clothes clean.
The bike survived the flights just fine. I managed to lose one of the washers from the handscrews/clamps while removing them; I simply replaced it with a nondescript washer later.
During the trip itself I folded and unfolded the bike a lot. It is a PITA to lug it up and down stairs all the time, but it's totally worth having the bike on the street
Once, while folded and sitting on the ground, I managed to tip it over to the side where the handlebar was folded. My light was clamped to the handlebar; when the bike hit the ground it managed to break the light off its clamp Nothing that some CA glue can't handle, I hope.
It was cool to check the odometer before and after the trip - "I would have had to walk *that* much!?"