The Breslmair Converter Cornet - Trumpet caused me strong, but mixed, feelings. Its design and finishing is amazing. Breslmair has thought in every detail of design, including a step right after the end of the mouthpiece, creating a seamless extension that transforms the cornet backbore into a trumpet backbore. The mouthpiece fits perfectly.
It must be understood, however, that this is NOT AN ADAPTER of a cornet mouthpiece into a trumpet, It is actually a CONVERTER, which TRANSFORMS a cornet mouthpiece into a trumpet mouthpiece. In other words, while other adapters (I have tested also those produced by Bob Reeves, Bruno Tiltz, Thomann/Gewa) preserve the typical "cornet sound" of the cornet mouthpiece and just allow its secure coupling into the trumpet, the Bresslmair converter transforms the sound of the cornet mouthpiece into a deep trumpet mouthpiece. The sound gets more brilliant, martial, powerful, like a trumpet mouthpiece, while losing the soft, delicate and dark sound of the cornet.
This means that this converter is perfect for cornet players who want to play a trumpet with a typical trumpet sound but without having to adapt to a trumpet mouthpiece. On the other hand, the Breslmair Converter is disastrous for the trumpet player who wants smooth the sound by using a cornet mouthpiece in the trumpet: all the beloved features of the cornet sound are gone.
Thus, depending on what you want to achieve, the Breslmair Converter may be a blessing or a curse!