Hi Lori,
I was the physio in a small trial using the PoNS for gait and balance rehab in subacute stroke. Here is the article:
https://www.sciencedirect.com/science/article/pii/S1935861X17308914
We found that the combination of physio rehab using the device was more significantly effective than rehab alone for improving balance (measured by the MiniBEST test). The difference was clinically significant, meaning the control group were below the cutoff for falls risk and the PoNS group were above.
The article talks about how it's thought to work and describes minor "adverse events". It doesn't mention that it also made some folks salivate quite a bit, but remember these people were post-stroke, not MS. I believe there are studies in MS out there.
I'd love to do work with using in for MS rehab, but it's not yet approved for use in Australia!