I recently purchased a Mel Bay book that contained Renaissance solos for the mandolin, which were adapted from late 16th Century English pieces for the cittern. The book says the mandolin and cittern were comparable in size and range.
Based on the description, it makes me wonder if the modern teardrop, flat-backed mandolins actually share more in common with the cittern than the historic mandolin (bowlback, gut strings, before wires). The cittern and these mandolins share a similar body style and metal strings.
When I found samples of what a cittern actually sounded like, it was not harsh (like I expected it to be).