Not sure what particular model the Conn is and what year. I would think pre 60's. I own a 24I which is a 1963 horn which has the odd sized receiver and mouthpiece. Not being a Chinese made horn advocate, I would go with the King 2280 as a non compensator. I have played the King and much better euphonium like sound than the Conn. There is also a VMI on Ebay which is made by B&S which is German made. I have a 4 valve B&S non compensating which I love and has a much nicer sound than the King and some Yamahas. Not sure if the VMI is a clone of my horn but it looks like it. I've never seen a review or comment on the forum about B&S so I am pretty much alone on my evaluation. I've also played the Wessex Dolce with my own mouthpiece and wasn't impressed and I stand pretty much alone with that as well. If you want my choice it would be the King.
B&S 3046 Baritone/Euphonium
Wessex Festivo
B&S PT37-S
Schilke ST20 Tenor Trombone
Jupiter XO Double valve bass trombone