I have a couple of Conn 17B Director trumpets, and I also have one 17A Director cornet (all with coprion bells, and all made in the 1960s.) Those are excellent instruments. They were marketed as student instruments by Conn, but they play as well as any of the so-called "professional" models that Conn made during that time. It is said that, prior to 1970, the C.G. Conn company didn't make any student instruments, and that all of their instruments were of the highest, professional level quality.
The smaller .438" bore of these vintage Conn trumpets (like the 17B) make it a bit easier to get up into the upper register (especially with the right mouthpiece), and also make it easier to play longer without getting tired. The coprion bell on the trumpet makes the sound more focused and laser-like (less spread than the yellow brass bell of the 15B director), and therefore makes the 17B sound more like a typical C trumpet (in my opinion), even though it is in the key of Bb.
The coprion bell on the Conn 17A cornet gives that horn a bit of a warmer, darker sound (very nice and desirable for a cornet to have), which is a result of not only the copper (coprion) bell, but this also has to do with the different bore size, which is also more of a conical bore (as you would expect from a cornet.)
I have a collection of several vintage Conn trumpets (1920s through 1960s, mostly and one from 1978), several different models of these, all with the same .438" bore (a.k.a. Conn #1 bore), and the Conn directors that were made in the 1960s are among my favorites. I personally prefer the 17B (coprion bell) Director for classical gigs and sometimes for jazz soloing, and I prefer the Conn 15B (yellow brass bell) Director trumpet for playing lead trumpet in big bands and similar commercial music.
So yes, it's a great horn! You scored an excellent garage sale find, for sure.