It makes playing them an absolute pain, when they should have good synergy, because they can both defend him.
Unchained, because he can blow you up.
Handmaiden, because of Focused Spirit. Needed for Power on pushes, because other Talents don’t give any or it’s applied after the push.
There’s also a bug/possible bad choice made with Engineer’s DMGR Talent being able to be FF’d too.