I been analysing again chain boost lvl5 weapons for noel/serah vs chain bonus boost II on monster's.
On noel/serah it seems to add a fixed % to the attacks so eg. if using sab/com on serah it is extremely effective eg. against ispusteke which has 100% chain resistance its almost as effective as using a rav without chain bonus boosts. I think this has led to people thinking its great to use on monster coms and I see it in the monster faq on com monsters.
However on monster coms it seems to add a % based on the chain bonus boost already inficted. So as such its a bad idea on monster com's.
eg. my com lightning with chain bonus boost II using ruin's against ispusteke simply cannot increase the chain bonus at all not even 0.1%, only maintain it. Whilst serah with ruin's increases it by 1.5% per hit. (with chain boost lvl 5 weapon).
Searching I find very little info actually almost none at all on chain bonus boost II algorithm, simply discussions of it been added to monster builds.
Chain Bonus Boost II is is not bad on COMs if you have room for it. CBBII is a Base modifier and such is affected by the chain resistance of the enemy. So against anything with 100 chain resistance such as Ispusteke, it will add nothing to the chain guage until the target is staggered. Against an enemy with 60 chain resistance (Raspatil), it will add 0.8 the gauge. Chain Bonus Lv 5 is not affected by chain resistance, so it will usually always add its full value per hit (1.5 for Serah, 0.75 for Noel). CBBII is definitely inferior to CB lv 5 but that does not make it useless.
http://etrosgate.com/ ~~~ The Gameplay Nexus for Fabula Nova Crystallis Final Fantasy
You have to click "SHOW" on the spoiler box to make the table visible. Chain Bonus Boost II does not depend on the ability used. There are numerous reasons why you could be seeing a larger bonus on a Rav, and I can't say which it is without seeing it myself.
Etro's Gate---The gameplay nexus for Fabula Nova Crystallis Final Fantasy http://etrosgate.com/