Just received and tried a Yongnuo 8-AA pack. Attached to a 550EX this inexpensive ($45) pack is slower than my Godox 820, which is around $140 delivered where I live (many sellers will not ship such items to Hawaii). Not a scientific test. I used 8 freshly-charged PowerEx AAs right out of a Maha charger. The batteries inside the 550 were also just charged.
Cost difference mitigated somewhat by the necessity of buying eight rechargeable AAs to run the cheaper unit.
One benefit unrelated to speed is that longevity at an event, for instance attached to a balcony over your reception area shooting area. And Yongnuo repeats over and over the need to avoid rapid shooting of 20 or more exposures -- for the danger of overheating.
Perhaps others with both can add to this. I will try my 580 with the Yongnuo in a bit, and make a more quantitative comparison.