The Pro is currently mounted on the Petzl proprietary helmet adapter. I taped 3M Dual Lock pieces to the adapter and the helmet. I secured the Pro with a cable binder.
The following second helmet light is fitted for demonstration purposes only. The grey/black one is the Petzl Swift RL Pro and is mounted "permanently". The White/Grey,Petzl Swift RL is using the Uni Adapt clips to demonstrate how to fit headlamps with straps to a helmet.
As both are used with the Reflective Lighting technology, they would both dim down, rather than add extra power.
The two Petzl Bindi are excellent urban bike lights. Lightweight 35g, 200lm for 2hours is plenty for urban conditions, most of the time I use the power saving low light modes.
Because of their red light feature, they can save both as handle bar light and rear light.