I am frankly not a fan of high break falls. Step outside and do a high break fall on the pavement. Besides the obvious results of such an adventure, the high break fall keeps me from staying connected to the nage so that I can continue my attack.
I teach students proper ukemi. Maintain a connection with the nage, Conform and dissipate the force so as to first, learn to change levels safely; secondly neutralize the incoming force; finally, return the force - all while maintaining your center and structure. If you are doing these things correctly and you are thrown in such a manner that you really do have to do a high fall, your body will conform to the forces so that you do not get injured.
Launching yourself into the air breaks the ki flow, which tends to increase the risk of injuries when being tossed on hard surfaces. I have done sacrifice throws and have been tossed on hard wood floors and pavement without bruises or injuries because of the above-mentioned factors. Not many people want to try practicing that way very often; I wonder why?
I know the posting is quite old, but well...
Actually, I've done breakfalls on every kind of floor. Tatami, sure, but also lawn, wood and, yes, concrete. No pain at all (excpet on asphalt it will probably abrase your skin, but then a forward roll would probably be worse...)
And in our direction, I don't feel at all that the fall breaks the connection. On the contrary, it's quite often the only way to follow the technique through. But maybe that's because we never "launch ourselves into the air", we're just thrown and follow, which, depending on the throw, results in the breakfall. But Carsten has already written a lot about that, I think.
For the teaching: in our dojo, we normally teach it when people want to learn it, which can be after a few months if you're confident and fit (my boyfried was really eager there...
) or after years. A lot of people start at quite an advanced age and are not too sporty for that, so they tend to go slower. And some never get very good at it, which is completely okay.
But with an uke who cannot so highfalls, you always have to adjust your technique so it's possible to do a backward roll.