I bought this in February and found that it didn’t help with my dysautonomia/POTS, though I also have a diagnosis of ME/CFS, cardiac preload failure and small fiber neuropathy (all confirmed by a workup and iCPET by David Systrom at Brigham & Women’s). Poor venous return is a major issue for me, at least according to Systrom, so I thought the Hummingbird might help but was wrong. I used it for about 3 weeks straight and I found it made leg muscle fatigue worse, not better.
I am not aware of any doctor who specializes in POTS and autonomic dysfunction who is recommending the Hummingbird, though it is admittedly fairly new to the market.
It is also quite expensive for what you get. It seems like it should sell at Bed, Bath & Beyond for $40.