Yes, I agree. I tried different bots over a couple of weeks and my conclusion ist that you do not gain significantly (sometimes you even lose), the only ones really profiting are the bot operators.
So, if you're only in for the money, I must disappoint you. However, they can be used to create a little more exposure by pushing your article up in the hot or trending sections. But this is another type of investment...which by the way could also be done by spending some money for promotion and then show up in the promoted section.