Has anyone investigated the use of an oxygen generator rather than carrying an O2 cylinder?

According to this study from sea level up to 18,000 it seems to work. http://oai.dtic.mil/oai/oai?verb=get...er= ADA371747

"We conclude that from sea level to 18,000', molecular sieve based O2 concentrators are capable of providing medical grade supplemental O2 for at least 8 hours."

Pricey but for those the fly with O2 every day then over the long term it would be cheaper as there would be no refills. Here is a unit for $3K. http://www.emedstores.com/xpo2-porta...extra-battery/

Might they be less dangerous in an accident? Is battery power an issue?

- John