If you have dim light, I'd use shadow blade every time for advantage.

I'm not a fan of the lost round if haste drops. Maybe blink will save you - if you casted it. If you happen to dip/multiclass rogue, the choice is even easier (as you can disengage with cunning action already).

The ac is nice, but how nice is a third attack? Until level 14, probably not that nice.

Later on when you feel safer about making most con checks, sure. Of course; once you can get 5d8 out of shadowblade - that's a lot.