Iâ€™ve had one of these (SBâ€™s) for 6 months or so. Pros- is fairly quiet. Can hear yourself in noisy environments with the earpieces or whatever you use. Cons- restrictive in the upper register so best used for softer, low to mid range stuff. (If you are trying to do range-building exercises-say for instance Claude Gordon etc., would be better to use a more open, less restrictive mute or play open (best) The amplified sound is similar to an amplified straight mute. (After all itâ€™s still a mute) It picks up sounds from the valves. Iâ€™ve had a â€œWhispa muteâ€ for many years. I think the next practice mute I will try will be a Trumcor â€œLyric stealthâ€ model. I dont think the SB resistance would be "harmful" as such but its not a realistic playing environment so I would use it only whan I had to.