I never had much of a problem with glass lenses. Put many miles on vehicles with E-code headlights (basically the same thing as a sealed beam assembly, but with European beam pattern and a replaceable H4 or H1 bulb instead of the unitized halogen capsule.) Some of those lights have outlasted the vehicles on which they were first installed.
I have had to replace at least one composite headlight due to fogging and finally bad condensation inside the reflector.
I can't remember ever having a physically broken headlight...
nate