I did both (active and passive) and I saw very good results. I think it’s most usefull to use the tent only for stimulating RBC production. For this purpose you don’t have to go that high, but you need about 200h (3-4 weeks) of time spent in the tent. I was shooting for a SO2 of 90-92% in the morning. That doesn’t impact sleep qualitiy and recovery too much. The active part (walking on a treadmill and breathing the air from the generator) is a bit more tricky. That’s highly individual and every person has to figure out how much she can tolerate. I saw SO2 as low as 60% and also passed out once. I found myself lying behind the treadmill. At first I didn’t know where I was, but fortunatelly the mask was stripped off my face;-) But I saw good adaptations and felt stronger with every workout. Part of this is also that you lern how to breathe correctly. But the breathing is almost the same as at real altitude. You have to be quite focused.
I have a friend who has great knowledge in the field, both practically and also scientific.
unfortunatelly his website is only German. But for everyone who is really interessted in this stuff, feel free to contact him directly. His English is not too bad (for sure better than mine). I know that he is developing some cool test methods to figure out the individual response to altitude and altitude training and preaclimatisation. We agree that this won’t be of much use for highly trained individuals (at least in the beginning) who have a very good feeling for their body. But it should give the recreational athlete good data and a guidance of how much hypoxy is needed. A lot to come in this area.
So, breathe as if your life would depend on it!