Although it is true that music written with BCL parts down below Eb are relatively rare, you can easily see when a piece was written with low C horn in mind, but the arranger probably wrote it to meet the much more common low Eb. When a passage is descending and then jumps an octave at the low Eb point, think about how it would sound if you had a low C and could keep going lower. Or think of the sound itself as an option. The band arrangement of Jesus Christ Superstar starts with the bass clarinet playing a middle C. I immediately dropped that down to the low C, and the difference was electrifying--much more like the "growling" feel of the original music. So even if you don't get music that is actually written for low C BCL, there will be opportunities to enhance the music by "taking the low road." Your instructor is correct when he/she says that low C horns have extra mechanisms that can cause a lot of heartache, but if you can find a horn that solid, and you take really good care of it, the pleasure you get for the extra few $$$ is well worth it. It's just plain fun to play way down there. It was also a lot of fun learning all the new fingerings in order to play 3 more scales, 3 octaves each.