I'll cut right to the chase: It's my opinion that individual health bars appearing above enemies should not be implemented. They clutter the playing field and make the Spiral Knights look more like a generic RPG and less like a free-flowing action game. They also make the game even easier, which is not what is needed at this point. Adding an option to turn them off won't help, because players who disable them will lose a tactical advantage. It's like Detective Mode in the Arkham games; the game looks better with it off, but players will typically miss tons of helpful information if they don't keep it on.
The health bar in the corner of the screen for the last enemy the player attacked is a decent addition. My main concern about it is that it looks like a case of dumbing down the game by basically shoving enemy health, type and weakness in the player's face. I'd make it significantly smaller and take out the weakness part. That way it could actually be a cool addition to the HUD.
You will be able to turn them off.