I believe u r gonna find this a "loaded" question... using the rubber grommets & brass eyelet doesn't change anything u will notice in flight. Some like it for absorbing vibration.. especially on nitro models... others don't use them at all & just hard mount their servos. Ultimately it's just a matter of preference. I personally use them on all my models. If u do use them, the side of the grommet with the ring goes against the heli.