Joining bounty's is most likely having a probability work and it's not guaranteed that at the ending you would be paid something tangible or similar, though most of them maybe or may not successful at last folding up leading to waste of time and energy to promote them. Alternatively if they succeeded then you get paid and having something good from the project.

So it's your decision to choose from the trusted bounty's you wishes to or following some reputable managers then you could get big chances of earning from bounty.