I never has use one myself however, in order to work, the floating lid must be a bit smaller than the inside of the tank, so that it floats down as the liquid goes down. That would indicate that it does not eliminate exposure to oxygen. For a high volume user, may not matter. For lower volume user and or more assurance of no air contact, use several smaller glass bottles filled to the brim or topped off in nitrogen gas, is a better solution, and probably less expensive to implement.
Glass bottles aren't very practical for large volumes that are gradually reducing as working solutions get partially discarded. I also don't have nitrogen and would have no clue how to get any.