Question about etoile guard?

do i need to guard when uing double saber or soaring blade?

no but is highly recommended to do it, Etoile gimmick attacks can only be used by weapon action and perfect guard does activate those bonus too giving you a huge counter damage boost.

Not an expert but i'm assuming if you want optimal dps rotations you'll want to use them. Especially when playing soaring blades as all of its attacks and PA's are quite slow. Guarding with it also boosts your gear meter which lets you use connect/full connect often. and full connect is where you do a truck load of damage.