Some band director in the past was obviously sold on Kanstul marching brass, as the school owns a few of several types (mellophones, [now: mostly obsolete] marching French horns, and marching baritones). I remember when the Kanstul marching brass first hit the market (originally G instruments) and made a big splash, but I never saw any of them (neither the G stuff nor the B-flat / F stuff) - so I didn't know anything about them. The first one that I repaired for this school was a mellophone, and - prior to repairing-then-playing that instrument - I always viewed King as making the best mellophones, but I have to say that that Kanstul mellophone outplays King.
Today, I put back together a previously pulled apart Kanstul marching baritone; it's one of those with a thumb ring to tune any note (which I consider to be a good feature, but I doubt if many students ever used the feature on the various makes that offered it). That issue aside, once I had that instrument all back together and doing what it was supposed to do, I was really impressed with it as well. FWIW, the mouth pipe featured a standard shank receiver. The lower range is a little bit more sparkly than several of the other makes which are currently out there, (certainly more so than Yamaha, and - repair-wise - I'm pretty tired of messing with Yamaha marching baritone valves and their guides).
I was never a particular fan of and of the Kanstul concert instruments - whether they were any of the various tubas or trombones or those Benge-like "French Besson" trumpets or even the compensating euphoniums, but to each his own.

I have to say that these marching brass instruments - which I've finally encountered - play exceptionally well.