Here’s the difference between Haku and Len though.
Len was officially recorded by voice actor Asami Shimoda as stated that it took 25 hours (4 work hours) to record all the appends for the Kagamines.
Here are some quotes from Asami.
Shimoda fact, without knowing until just before release, to hear from krypton’s me “is phosphorus and Len” before receiving an interview with a magazine, and “that it was good ‘s not Ken” and I was relieved. At the same time, I think that me “Thats good me Len!”. To initials is L and R, but it is also good sounding sound.
── Why do you do one was to “Len”?
Shimoda anyway I was told for two persons voice. and that want feel that one person is known by different voice.So, you can have me with his personality, which is divided played the voice of the boy’s voice and the girl wanted to Na I was me casting, I I was really happy.
Haku on the other hand, “was originally made as a representation of songs that use Hatsune Miku but ended up sounding awful. In such cases, the makers of that music would then proceed to whine about how their work never received attention and later moved on to whine when criticism stated their work as dull and boring, or was posted quite late when few people were on Nico Nico Douga.”
Yes, Rin and Len do sound alike. However, with one voice actor voicing two characters at the same time, it’s bound to happen.