Anything that stops dust or insects such as fruit flys from getting in should work for barrier purposes. For allowing the CO2 to escape..... I would think the saran wrap with a rubber band wouldn't be exactly airtight and would allow the gas to escape.
The only advantage I see over the lid is it's cheaper, no airlock needed, easier to clean when done and you can see the fermentation.
The only disadvantage I could see is if plastic wrap allows O2 to diffuse into the bucket. I doubt this is an issue, however, because of it's ability to maintain food freshness and the CO2 present is heavier.