Need help on the justification to dip 1 hex

Looking to do another honor mode run with friends and am very keen to try the 11 EK/ 1 hex blade but I can’t understand the main draw.

Do I need to bind a weapon to my main hand for it to count as a charisma weapon? If I do this with shadow blade will I lose the psychic damage?

Do you take it for the spells? Should I respec at lvl 9 to get the spells I want to optimize?

I’m looking into going pure shadow blade, although I’m thinking about using shield in my off hand to stack survivability instead of damage.

Any information and the mechanics around it would be greatly appreciated!