Interestingly there are no rules on what kit is actually used just that you must use O2 at 10,000ft.
I use the mountain high O2D2 unit which will give 36 man hours from a 2.2l cylinder more than twice the nearest competitor.
You should buy the kit with a Euro cylinder not a US DOT spec and with a DIN477-9 fitting not the US CGA540 thread. This will make it easier to fill in Europe.
The MH kit comes with both cannulla and face mask. The rule of thumb is cannulla are fine to 18,000ft and then a full face is required.
PM me for details.