I’ve had one of these (SB’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 it’s still a mute)
It picks up sounds from the valves.
I’ve had a “Whispa mute” for many years. I think the next practice mute I will try will be a Trumcor “Lyric stealth” 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.