The Six Duos Op. 50 for Trombones were originally written for two Cellos by Offenbach probably as teaching aids or for a light chamber music selection for an evening soireÌe. Being a Cellist himself, these works were most likely first played by Offenbach.
The Six Duos contain over 50 minutes worth of music and are appropriate for intermediate to advanced performers.
Both parts have f-attachment notes, but are not mandatory, as Mr. Sauer has written alternate ones.