If not mistaken, the actual i-roomba from i-robot is just running through the floor randomly. It covered almost the whole surface because of long time operation. There're still some place where it missed. I'm not sure about the latest i-roomba or any other model, but the old ones doesn't have mapping algorithm at all.
PR23 alone seems like not a good solution for your application unless you make some modification to it. You will need to eliminate the deviation error of the robot while moving around coz i cant see any feedback sensor like encoder at the motor part. I believe this kind of modified rc servo cant give you constant performance. For example, this robot may gradually move to right hand side even when you program it to move straight forward. You can have a try and see. If it cant move in the way you want, you cant cover the whole space even you applied the best algorithm to it. Of cause i'm talking about a perfect outcome. If you don't need 100% coverage, there's nothing to worry about it