Has anyone ever use Willer Japan Bus Pass?

So im planning to travel from tokyo to osaka then osaka to tokyo, and also planning a day trip to fuji. If i buy individual ticket it will be around 18000 yen, while the 3 days pass only cost 12000 yen. I want to buy it but i never it about this pass before. If anyone ever use it, is there any drawback to this? also the does the pass count departure and arrived date? because im planning to take a sleeper bus.

Thank you