We honestly don't see a lot of those going bad. I only stock maybe 4 or 5 alternator part numbers at any time. That being said we can usually get Motorcraft same day or overnight.
If I had a vehicle with known alternator issues and I was in there doing something else I might consider it like on one of the Powerstrokes where pulling the belt is a pain. Or something like a Terminator Cobra where they are a pain to get to I might consider it if I had the belt off for something else.