Some reasons for broken balancers...
I broke a few before I got my BHJ... Here are the main reasons you keep breaking them (in my opinion):
1) Ford stock balancers are poorly designed (that's a polite way of saying they're a piece of $h!t)
2) Stock balancers are meant to be installed once. If you remove it and reinstall, or if you install a used balancer (junkyard, bought cheap from someone, etc.) it will fail. The aluminum "sleeve" distorts and weakens when removed and reinstalled. (Been there, done that...)
3) Balancer bolt not torqued properly. Requires 110ft/lbs, best to do in three steps (90, 100, 110).
4) Installation of balancer with used bolt. The bolt will distort when torqued. Used bolts will either break or come loose over time and allow the balancer to "walk" on the crankshaft.
It is worth every penny to get a BHJ balancer. They don't break, and they can be removed and reinstalled if necessary. Just remember to always use a new bolt (BHJ balancers require a slightly longer bolt than stock), and torque it to the proper spec.