I'm sure you're right, but the reason I know about them is that I do know a guy who used one, and got a "better" prison. No names, for obvious reasons.
While incarcerated, half the people "know a guy". Maybe the prison was "better", or maybe it was just a different mix of pros and cons.
Not only was the advice I received unhelpful, following it actually made my stay longer. My family would have been better off taking the substantial amount of money and setting it on fire.