In the old field manual series, I don't recall if I have seen them in the more recent FM:update X books, each of the various units had different abilities. It seemed a good way to add value to each force as it helped a Ghost regiment look and act different then a davion heavy guard unit.
The FMs also assigned a rating for each unit's equipment. Were these rating and unit abilities balanced in any particular way? Were players required to pull from mechs and vehicles that were equal to their rating and below? If so how did that work in later eras as new TROs were released after the FMs were printed.
Are these FM abilities still valid?
They're as valid as you want them to be. I feel the equipment ratings and special abilities added flavor, but not balance. Balance was up to the person creating the scenario and/or running the game.
Also, if they have been replaced with stuff in Campaign Operations, which I suspect that they have but I wont have time to look through it again for a few weeks, how have those worked out? Comparison between the two for those that have used both?
They have been updated in
Campaign Operations, meaning those that specialize in night ops probably still specialize in night ops--the rules for those specialties quite likely have been tweaked or changed outright. There are actual rules for assigning special abilities in this book. I don't have experience using them, but that's a pretty good sign there's at least
some balance.
I did a quick check on
Field Manual: Draconis Combine vs
Combat Manual: Kurita. Though these products cover different eras, you can see similarities in the abilities.
FM:DC1st Sword of Light -- Specializes in night missions. During nighttime conditions, unit members receive +2 initiative modifiers and do not suffer the +2 to-hit modifier that standard units receive during night combat.
3rd Benjamin Regulars -- When fighting in Flatlands terrain, they receive a +1 initiative bonus. If they field twice as many units as an opponent, the bonus increases to +2; if they field three times as many units, the bonus is +3; and so on.
CM:K (Special Command Abilities)
1st Sword of Light -- Banking Initiative, Environmental Specialization (Night), Esprit de Corps, Focus (Nightwalker)
3rd Benjamin Regulars -- Environmental Specialization (Clear)
[no initiative bonus allowed for this one], Tactical Specialization (Engineers)