I bought the Trumpet
Silent Brass system in 2003-4. This may not be the same model as the SB7X. The Silent Brass system provides a mute on the projecting qualities of the trumpet
. As a practice tool, the Silent Brass is nifty for late practice sessions, apartment dwellers, and last minute hotel preparation.
I only have used my Silent Brass system a few times. The amplifier/headphone setup is pretty cool if you're into that. I used it during late hour practice at our condo, usually just for chop exercises. The model I owned was somewhat "dense" and despite claiming a natural feel, often still felt like the backpressure of a mute.
I give the Silent Brass system 3/5 for personal experience. It's useful if you have the need, not extremely so without. If the SB7X has done away with the tight airflow problem, it earns an automatic 4th star for ingenuity.