I personally have rented/used the tool--------------------GET EXTRA RIVETS!!!!!!!!!!!!!!
It is EXTREMELY difficult to position/use the tool if the axle housing is in the car (but it can be done). So, if you have the housing out of the car, now is the time to install them.
The reason that I strongly recommend getting extra rivets, is because it is quite likely that you will mess up 1 or 2 or 4, especially if the housing is in the car (you will experience a self taught learning curve).
Furthermore, there is (or was) a time limit (without extra charges) on the rental time, so don't rent it until you are actually ready to use it and then return it.