Go for the Ld2. I use two of them and they are wonderful. The main advantage over the P3D is that they take easy to find and cheap AA rechargeables, and work just fine without futzing around with them.

Weight isn't an issue for the one I have mounted on my helmet, it weighs just 117 grams with batteries. For comparison the lamp head of my Cateye DoubleShot weights 141 grams without the mount.

They also have a longer run time than the P3D.