I did this in March this year and had about 5 sessions lasting about 45 minutes. I used a chamber that was part of an MS centre and we didn't have to pay if you had a crappy condition like MS, Neuropathies and brain trauma.
Many people with MS and brain trauma I spoke to felt it really helped.
At the time my sfn wasn't good but it wasn't as bad as it is now. I didn't feel much different using the chamber but I can believe that enhanced oxygen levels could potentially support good nerve health in theory.
I am really unsure about paying substantial amounts of money for this. I don't believe it could arrest sfn. If the charge were reasonable I would say it's worth trying but I am so scepticle of private organisations making false claims without the evidence to substantiate it