A few of us old timers use them. I Recently bought a large lot of Westinghouse #5's to do a personal project. I'm going to use them with my crown graphic and Rollei. The M2&3 bulbs put out a reasonable amount of light but only sync with a focal plane shutter at slow speeds. Most cameras no longer have M or FP sync for bulbs. Bulbs have to fire a fraction of a second prior to the shutter opening so it reaches full output when the shutter does open. Bulbs don't Fire instantaneously like a strobe which has no delay (X sync). Bulbs have a material like zirconium and magnesium that ignites when electrical current is passed through it. It takes a fraction of a second to reach the output peak. Some bulbs have extremely long peaks like the FF33 which was designed for high speed motion picture work and has a peak of 1-3/4 seconds. Most bulbs are a fraction of a second. Focal plane bulbs require FP sync and require a different advance time to ignite than M class bulbs. It's longer as I remember and the peak is longer so the FP shutter can travel for the full exposure during the period of maximum output.
AG, M2&3 are less popular due to lower output compared to #5&25.
I used a lot of bulbs back in the 60's and 70's. I've lit large interiors with the huge and powerful #3's, 11's and 40's. These screw into a regular light socket and can be fired with 110v AC. Don't try triggering other bulbs with that high a voltage. They will burst and you'll damage your shutter. To use 110v you need a special relay box with low voltage going to the shutter. 110v fed to your camera shutter will destroy the shutter and possibly destroy you too.