I had been using Breakfree since 1990. I used it because that is what I used in the service. It had worked well for me up until a few years ago when I started noticing (that when participating in Tactical Carbine Courses, 3 gun matches, Department training) the Breakfree would start to gum up the bolt of the AR15 and after gumming up the bolt would start to sieze. The gumming would start between 250 to 350 rounds, and the rifle would usually be totally siezed up before I hit the 500 round mark. In most of the traning classes I attend it is common to shoot 500 or more rounds in a day. Having been in the Marine Corps I am pretty anal about cleaning my rifle, but when you shoot 500 rounds in a day you don't have time to stop and clean the gun, and there is no reason why the AR system can't go well beyond 500 without a cleaning, especially if all that shooting is done in one day. I had never had problem with shooting 500 plus rounds using Breakfree in the early and mid 90's, but was told that Breakfree changed their forumla back around 2000 (give or take a year). If I remember correctly I was told that they started adding some kind of teflon and this is what causes the Breakfree to gum up after extensvie firing.
I have since started using FP-10 and no longer have the problems with the bolt gumming up or siezing. I would highly recommend the FP-10 over the Breakfree.