The EXT 120 is a great ozonator.It is built by Azco, the same makers as the POG. It would be a good choice for the sauna and for all other types of ozone protocols.
Your oxygen concentrator will work nicely for the sauna but not for too many other ozone protocols because it will not give you slow enough flows of oxygen. There is essentially little difference between a well-maintained oxygen concentrator and bottled oxygen. Concentrators give you dry oxygen within a purity range of 87 to 95% pure O2 while tanks give you purity of approx 98.5% pure O2.
Hope this helps