I would expect it to sound like a bugle, but with a capability for more notes.
The tone of brass instruments is in a large part created by the shape and the size of the instrument. A trumpet does not sound like a cornet. A standard bugle has a different tone compared with a trumpet played without using the valves. A flugel horn is essentially the same shape as a bugle, but slightly larger and with valves added. It has a more mellow tone than the trumpet or cornet.
Quack!
GtD.