It is way more dangerous then some are trying to sell it.
Oxygen toxicity is a possibility of course.
But don't forget the dcs itself..
One examples:
Last year 2 divers surfaced with a little deco, way to fast. After a few minutes they dropped back down and did continue/recompress their deco.
Both died. With gas still in their tanks in only a few meter of water. Dcs hit them both and they were not able to go back to the surface. At the surface they might have a chance by going to a chamber.
It's only a tool for a highly experienced and equipped team. Support divers, full face mask, gases, maybe even a habitat. And only if there is no other option. It is very very dangerous