I have tried and expertmented and i belive that they are better in a half deck. my main and probably only reason why is simply because their clan bonuse. u cant stack poison. period. making into a half deck will give u poison and a better clan bonse like +8 att or +2 damage etc.
Full mono no, freaks work best as mono + leader or in 1/2 decks. They work well with morphun IMO, also with atk clans and roots. These work for me, not sure about you. Also Dmg reduction goes with them too, thats why I use roots with jeena 2* or arno and yookie. pussycats would work well too although it can be expensive to maintain and requires almost perfect pilling.
Yes, the Freaks are suited for a split deck and nothing else. Their clan bonus cannot be stacked and needs help from another clan, such as a attack manipulation one. Combined with their poison, your other clan can attack hurting your opponent more.
If poison was stackable, they would hit #1 clan in ELO a long time ago.