Ernst Mielck's '2 Impromptus' offer a glimpse into the late Romantic style, characterized by clear melodic lines and pleasant harmonies. These pieces are likely less complex than some of his contemporaries but still rewarding to play.
Work on evenness of touch and legato in faster passages.
2 Impromptus is rated Henle level 5 of 9 — late intermediate repertoire, roughly ABRSM grades 6–7.
You should be comfortable at Henle level 5 — meaning you can already play level 4–5 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
2 Impromptus is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.