More likely, they removed M class stars from filters because they primarily hold frozen rocks around them, if the primary star(certainly in my experience).
I do leave K types and some below that in just in case something curious pops up, and it seems that the main star can have an effect on terraformables or Earth-likes/water worlds even on the secondary(eg main is K, secondary is M with a bunch of terraformable HMCs). Or, another example, a T class dwarf orbiting at the barycenter of an F class and some other star at a distance of about 3.6k ls. Said T class dwarf held a terraformable water world at 15 ls distance to it. Probably one of my neatest finds to date. Another… terraformable HMC near a white dwarf(it was tertiary in the system, iirc). Not quite sure whether to call that second one prime real estate, though.
Sometimes get that temptation to toggle the M class back in just in case something curious does pop up with them. Most of the time, though, it doesn’t.
Anyway, if your brain says go scan that valuable world 500k ls out, and you have the patience and time to spare, I say why not? Mostly ends up becoming a matter of patience for me, though, rather than monetary or time investment. Not like you can do a lot during that supercruise trek.
I'm filthy rich and already Elite in Explo so I do what amuses me. It's mostly random anyway, some star types are more likely to produce earthlikes but if everyone is doing the same they're missing out on the unlikely ones (like the ones around neutrons which are probably more interesting). Found a few orbiting Ms because people were too good for them? 
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