I don't have my reference material with me right now, but here's what I remember sbout those three flash bulbs. Correct me If I'm wrong, folks...:

M2 is, I think, an instantaneous flash with a long period of sustained light, primarily for focal plane shutter use.
5 is the most common bulb out there with the bayonet mount, good for middle distances and for most situations. There is a blue version of it for daylight film- can't remember that number... 11?
25 is a bigger, brighter bulb, for maximum coverage in terms of distance and wide angle work. Sort of thing you'd use in an auditoreum.

Not gospel, just the product of an often faulty memory. I'll try to get an early 60's guide to you by tomorrow.