in what form did you submit your custom prisoner?
They had a selection of head and body sprites you could choose and then you could submit an optional text backstory as well as a name for your prisoner. In the game, when a prisoner arrives, the game would choose from a large list. The choice would be added to a machine generated personality and criminal sentence.
I really like this reward, it's easily my favorite reward out of all the indie games I've supported. Even though it's a small thing with no real effect on game play. There is an option menu where you can search through all of the submitted prisoners and flag one "this is me" so the game would always select that prisoner when you are playing.
Compare and contrast that reward to the crayon drawing reward that the Dwarf Fortress creators used to send to each backer. In that case, each donation would create a new task for the developers and the output of that task is nothing that adds to the game.
I would likely back your project just because I've had so much fun playing UnReal World and I'd like to see what else you come up with.