When use mast strobe light?
Honestly. If I was going to cary a strobe for this kind of emergency signalling, I would carry a completely seperate unit, with independent battery power, that could be hoisted up the mast at will. That way, if I need it because my other powersources have died and I do not have other lights, or my masthead light has been blown off the mast (has been known to happen) or any number of other nasty things have come to pass....well, the strobe can still function, for what that''s worth.
We have a $40 unit that I have attached two hose clamps and rings to. It takes less then 30 seconds to activate and hoist up the mast on its stick in the practice run we have done.
It makes much more sense to me then paying an extra $150 in order to put more weight permanently at the top of your mast, with all the potential for blown bulbs and fried wires that this implies)