you may want to a take a look at:

http://www.crossbow-review.com/Revie...k20C_page1.htm
http://www.crossbow-review.com/Revie...ok08_page1.htm
http://www.crossbow-review.com/Revie...stonTracer.htm

But I think this one single picture will answer your questions:
http://www.crossbow-review.com/Revie...r/DSC_0348.JPG

Yes, Firenock is the brightest offers a centered led and replaceable battery(now in many colors also)
Easton gives diffused light non replaceable battery
Lumenok mechanical activation, opne piece non replaceable battery

Mirko