Weidinger referred to his new invention as the “organisierte Trompete,” which came to be known as the “keyed trumpet.”
James Keller writes, “The tone of Weidinger’s keyed trumpet was far less penetrating than the brilliant sound of the Baroque trumpet, and its timbre was sometimes compared to that of a clarinet or oboe. It blended nicely within the orchestra, and it gained a devoted following among trumpeters for several decades, especially in Austria and Italy.”
Modern trumpet players use the E flat trumpet to play the Haydn Trumpet Concerto since it most properly represents the timbre that Haydn had in mind when he wrote his concerto.
Furthermore, the concerto was written in the key of E flat. For trumpet students unacquainted with the E flat trumpet, though, scores of the concerto in B flat are available (learning to play on the E flat is well worth the effort, though!).