Question about B Duel Flying 3

No it works at any merge count. You should only use it if you put it on a +10 merge

BST is total stats before merges and all skills (including weapons and seals), while "treated BST" is total stats before merges and all skills EXCEPT for the BST treatment effect of Duel Skills (i.e. the +5 HP doesn't figure into the BST).

No, the Duel skills work at any level of merge, because they alter the treated bst prior to merges. They basically change the "order of operations" for arena's bst and score calculation. (They figure in twice, once in the "bst calculation stage" and once in the "SP calculation stage" with their 300 SP costs.)

And yes, B Duel Flying is the same as the other duel skills in every way. This site is wrong.

Duel skills only makes your unit count as a 170 bst unit in arena, it doesn't increase your stats to a 170 bst only gives you 5 hp, you can put it on any merged unit but if you are going for arena scoring you want to put it on a +10 unit, but if you are building a Blue flier that's not yet +10 it still works just fine since they will still have the 170 bst for arena just not scoring as much do to lack of merges