Any string silencer will help, I personally like the yarn or fur ones myself over anything rubber. The rubber always makes a swooshing or whipping sound. Most likely from the rubber stretching and then coming back. The yarn or fur ones are a bit quieter. They do have draw backs when hunting thick brush or in the rain though.

I would not own a bow without silencers on it, even if it was a target bow. They help take the vibration out of the string.

As far as speed loss, depends on how heavy they are and where you put them. Put them in the right spot and you will hardly lose any speed, might even gain a few fps. It takes some experimenting though, and sometimes you need to compromise and give up some speed for maximum quietness, or give up some noise for the extra speed. The closer you get to the center of the string the slower it will be.

The difference in speed will only be noticeable on a chronograph though. Without one you will never notice the difference. It is not like it will change your speed so much your trajectory will change or you will need to change your pin settings (maybe at 60 or 70 yards).

If you want to spend the money a STS costs and hang that sucker off your bow feel free, but you can get it quiet for less than sales tax would be. And in my opinion it would be more quiet.

Paul