Actually on the inside they are not the same at all.
RPL uses 2.5W IR diode vs 1.2W diode on the PPL.
RPL has higher quality crystal to accommodate the larger diode.
RPL is ~1 inch shorter (battery related as the lithium cell is shorter than 2 C cells.
RPL uses a better driver board and with the battery protection circuit that also has ESD protection for the diode.
On the outside, they look very much the same and for given power rating, they perform equally well.....Wait, not quite true, the RPL also has less divergence than the PPL.
Basically the RPL is the 2nd generation of the PPL so to speak.
I just got a PPL100 and it is one nasty bastard. It wastes baloons rather quickly, almost instantly. The beam lights up a room and you can see the beam in a lit room. I call it a "ghost killer". If you are looking for a laser to get things done with, go with this one. Optotronics has a superior product, and it isn't wimpy like most others, and worth every penny. I'm using Duracell C 2500mah rcbats, they are the MINIMUM this thing requires. get 5000mah and you will see what it can really do.