Jazz trumpeter Clark Terry displayed his circular breathing technique many years ago, during a concert. He was the guest soloist with our junior college jazz band. I proudly showed him my trumpet, which was the same exact model he happened to be playing at the time, a Selmer Radial 2.
He could keep playing forever with that circular breathing technique.
I tried practicing it, but could never get the hang of it.
BUT, I guess if it was easy, all brass and woodwind players would be doing it.
I started my brass adventure in 4th grade with my great uncle's Holton Cornet. 1909 vintage. In 1969 my dad was headed out for another round in Vietnam. He set me up with a new brass bugle for use with the scouts and a new Holton trumpet. The trumpet was very sleek next to the cornet, but the narrower tubing produces more back pressure. My middle son played that trumpet through elementary and high school. Last year I ordered a fluegelhorn from Austin Custom Brass. They buy Chinese knockoffs and upgrade them into fine instruments. I like the bigger bore. Lower back pressure and mellower tone. 7 cases of pneumonia have wrecked my lungs, so it's a challenge to play. I suspect that mastering circular breathing will be more important with the lung problems.