"BEM" is a disappointment for stupid reasons. All it would have taken was a little smart thinking. BEM is a colony creature and as such he needed to be shown in a smart manner. As soon as you start seeing his body parts going off on their own every which way the character's credibility is completely shattered.
Greg Bear's novel Anvil Of Stars
is one good way to depict a colony creature and if TAS had done this "BEM" would probably be remembered more fondly.
Curiously TNG did a first season episode very much like "BEM" called "Justice." It also bombed but for completely different reasons.
Too bad because in both cases there is a worthwhile story buried within each.
"The Infinite Vulcan" is another cool story and very visually exciting episode...until you get to the fifty foot Spock and Keniclius. Then your brain gets a serious spasm of
If they had kept the clones normal sized then there would have been nothing to complain about.