The cabin portable oxy bottles are not of the same standard as the flight crew fixed masks and may not provide enough Oxygen under the ambient conditions or keep smoke out of your lungs.
I suppose it depends on your fit. Ours are of the same quality and will last long enough to keep smoke out of one's lungs for an emergency descent until the DV window can be opened.
Still it is a good discussion point, I see Airbus has no FCOM procedure that I could find and nor do our SOPs.