I have a P1D-CE and have tried it for cycling.
The size is good and it's certainly bright. The two problems that made me stop are the runtime on strobe, which is too short for my purposes (around 1 hour) and the batteries. It does not run properly on 3.7V rechargeables (not all modes work, goes to high on all modes, short runtime). I can't afford CR123A as $2 each. I did not try 3.0V rechargeables but I would be shocked to get 1 hour run-time.
It would be suitable for short rides and casual use only. The L2D is much better for daily use due to run-time and excellent support of rechargeable batteries.