Fantasy Sonata is written in the same virtuoso style as compositions of that period by Joseph Serafin Alschausky, and is fully idiomatic for the tuba or bass trombone. There is a passing 'reference' to the Concerto by Rimsky-Korsakov, and it is just possible that Schroen might have been familiar with that work as a trombonist himself. There are also some stylistic similarities to the Fantasia for trombone and organ Op.58 composed in the mid-19th century by Friedrich August Belcke (1795-1874).
This . . . work feature[s] several short cadenzas, contrasting dramatic and expressive sections [and] is in [the] Romantic style and appropriate for intermediate to advanced performers. - the publisher