With the recent airplane purchase I ended up with 2 of them. I sent both in for factory service, software upgrade, recertification. This one has just been refurbished and not used since I received it the first week in March. It allows you to fly in the teens and flight levels  for only one or two on-board tanks per year. https://www.mhoxygen.com/product/o2d2-x-str/   New,  these sell with regulator for over $1100. Pictures: https://www.dropbox.com/sh/zpf25jvui37z57s/AADCWnBrV