I have just tested the Amazon one above with my O2D2 and it does work in as much as the oxygen pulses do come out at the right time.
What I can’t tell is whether you get the same amount of oxygen out of it. I guess one should, because during exhalation one is not pushing air back into it (because the valve in the O2D2 is shut).
It will need to be tested at altitude, using blood O2 figures, against the MH one.
I have also written to the Amazon supplier (in Germany) asking if they do a cannula with a smaller tube internal diameter. If they reply I will report here. I am not holding my breath (so to speak 
).
@RXH – the German supplier you link to is selling what looks identical to the one I got. If you look closely, the tube has the same ridges on the inside.
If you look closely, the tube has the same ridges on the inside.
That is a good idea because I think it prevents the tube from bending, it gets internally stiffer. I have normal O2 tubes without ridges but with a green/red postive flow indicator which I always monitor closely at higher altitudes. It happens too easily that they get bent.
Peter wrote:
Obviously it’s still possible, with heatshrink sleeving / sealant.
Have you tried just to warm it and pull, so you lengthen the tube and thereby reducing the diameter? You could cut out the ridges before, at least at the end that you want to push over the adapter.
I got this reply
I am not sure if they read / understood my Q, however, since it was nothing to do with “quality”.
Peter wrote:
I am not sure if they read / understood my Q, however, since it was nothing to do with “quality”.
“Quality” in many contexts mean “kind” – or perhaps more accurately “according to some particular specification”. (That’s the ISO 9000 meaning of “quality”.)
Airborne_Again wrote:
(That’s the ISO 9000 meaning of “quality”.)
Actually, that is even broader. It means the ability to fulfil a task. Equivalent solutions are of equivalent quality.
But I think it isn’t too far fetched to assume the “public understanding” of quality was used.
mh wrote:
But I think it isn’t too far fetched to assume the “public understanding” of quality was used.
Considering the context (Peter’s question) I do think they meant “according to specifications”.
.. what would be the public understanding, I reckon.
The other approach to the “tube problem” would be to place the connection near the person rather than near the regulator. Then you can control the internal diameter along most of the pipe length.
The Q then becomes: for hygiene purposes, how far into the cannula might some “undesirable stuff” get?
