I had a BSX oxygen monitor before that company imploded.
I never managed to find any way to get meaningful data that changed my training. I think it is far too fringe yet to make it worthwhile. We are just now starting to find ways to train to running power with something like Stryd. I measured oxygen in my legs. It was less when I worked hard and more when I went easy. That is about all it ever seemed to mean. BSX suggested all these ways it could be useful when I bought it, but it never really panned out