One of my customers plays Russian music on a 19th century old guitar with a very thin neck. He wanted a guitar with the same body size and ergonomic feeling as a modern 6 stringed guitar. The clock key for string adjustment is a very precise mechanism mainly for optimizing playability. When traveling by plane the neck can be removed and the body will fit in a cabin case.
The idea with the hidden string was actually a estechic choice, but keeping the size of the head as normal as possible reduces unesassary weight. And the range of quality tuners is much better when it comes to 6-stringed tuners.