Quote from Perfectio;1090949:
Not worth it. The magic side of the equation loses so much in damage, while the fighter side loses 20% crit damage and some max. And more importantly, whike there is some synergy with fighter and some magic skills (shockwave, maybe Thunder) the two skillsets play at completely different speeds. Especially when instacast isn't up. There are some nifty combos there but Magic x Gunner and Fighter x Gunner are both much better combos.
It's not so bad. The problem lies in that in order to make use of 3 skillsets, you need to be heavily invested in AP.
One of the interesting combos I came across was:
Fireball (with the knuckles) -instant cast- - > Bullet Storm - > Bullet Rush - > Fighter Combos to finish off the survivors.
Other interesting combos is:
(Get hit by the enemy) - > Shockwave - > Fighter Combo - > Switch to lance -> Smash
Instant Cast Thunder - > Crash Shot - > Both Thunder and Crash Shot Lands - > Fighter finish
A korean player who has access to these knuckles wrote that these knuckles shouldn't be used as a main weapon in higher difficulties, but rather as an aux weapon... in other words:
You have your main skillset you mostly use, and these Merlin's knuckle makes super backup weapons. So it would be like:
Main: Lance
Aux: Merlin Knuckle
Main: Guns
Aux: Merlin Knuckles
Main: Range
Aux: Merlin Knuckles
His conclusion was that the Merlin Knuckles are great aux weapons to have, but far from the "ultimate" weapon. The unique ability it gives makes a great backup weapon that allows more flexibility in the main skillset if used properly.
Also, technically you can open "four" skillsets since you can sing without instrument.