http://www.lightandmotion.com/choose-your-light/urban/urban-850-trail

Pros:

1. bright
2. good light spread
3. price
4. lightweight
5. small
6. self contained
7. Li-Ion Battery

both PRO and CON:

The mounting system

Pro:

1. holds well to the bike (at least when it's new)
2. has extras for helmet and Go-Pro
3. adjust position easily to shine light where you want it
4. goes "easily" from one bike to another (since you have to take it off to charge it anyway)

Con:

1. a bit of a pain to get on and off (strong fingers required)
2. moves easily out of position when bumped (even if that is not really that much of an issue)

Charging

Pro:

1. Charges fast and easy
2. no batteries

Cons:

1. the "charger" it comes with is a short USB micro cable (that is it)
   I am using a tablet charger that I already had. If you don't have a high current charger it will not charge as fast

CONS:

1. included instructions
   It just has some cartoon/icons on the very minimal packaging that left me wondering about some things (would be fine if they had some good online instructions)
2. online instructions
   not much better but after trying things out I seem to get have the hang of it.
3. Color: Orange! ok, if you like orange you'll love it. I personally like all the colors of all their other lights but I don't like orange. It's not that much of an issue but how about black and silver if you don't want to offer multiple color choices per model?