There is a "philosophical" aspect to underlevers. Having all mechanical functions contained in the receiver makes engineering sense and avoids linking the forend with the action for cocking. Underlevers also avoid all that drilling and fitting of the spindle.
Arguably these quaint thoughts make sense to people who operate their guns by themselves, without the help of loaders.
Once you get the hang of operating an underlever one handed, trapping the stock under the arm and derpressing the lever, rather than using two hands to open them, they can prove surprisingly ergonomic. They behave like assisted openers.
The French went one better with the Ideal, but that is another story.
