I have just completed week 10 with the Powerbreathe.
This is my second week at level 5.5, and I now use a mini pyramid of settings each session. By that I mean 10 breaths at a low setting, 10 at a medium setting, 30 at my maximum setting, 10 at medium and finally 10 at low.
This makes sense to me, I think it teaches my muscles to do big full breaths at the low and medium setting, with a full load workout at my maximum setting.
I have just completed week 11 with the Powerbreathe .
Increased setting to 6.0 which is mostly achievable but not always. Still using a pyramid of settings in a full session (see above for an explanation).
At the start of my last week of the 12 week trial feeling it has been worthwhile. I will express a fuller view at the end of this week.