The guardian I shot had it already installed and Ive never shot one without an sts so i really cant comment on if it really makes a difference. The guy told me without it you could hear just a little string buzz but barely noticeable. Either way I would purchase the sts anyways simply because i wont have to worry much about arm slap on twisting shots with lots of clothing on. I also shot an ally and tribute both with sts and the guardian was noticably quieter. But taking nothing away from either. Both were SWEET shooters. None of them had any real vibration. The alley and trib both only had a little THUD sound. but no noticable vibration.