if you already have a P7 and want to supplement it with a light helmet light, then I'd recommend the Trustfire TR-801 which also uses a Q5-WC, but shares the same 18650 battery as the majority of P7 lights.
Well if the P7 lights came in AA/AAA versions and in the price range I would get one. I don't have a P7 yet but would like to get one later when the prices drop or when I have the funds for it.
For me right now a light under $25 is best but also looking to help others looking for a cheaper light if they can't afford the P7's and the whole charger setups.