FM is a big improvement on AM. I think Fleet used to supply 27mhz FM many moons ago. When those sets were current I was still a schoolboy, and they were limited to multi-channel sets which were way beyond my purse.
I believe the M-series sets had a very hot output, which explains their popularity with submariners. But these sets are over thirty years old now, and unless you get a set that has been little used they're likely to require refurbishment of at least some parts e.g. pots, swicthes etc. They won't work with modern receivers, so you're forced to look on the secondhand market and the servo standard was slightly different back then. They can be adjusted, but unless you're the type who likes to tinker inside electronics, I would leave them to the collectors and stick with modern sets, which have a few tricks up their sleeves the older sets lack e.g. signal conditioning, memories etc.
