I don’t know how it would be neater to use just one, because you’d have to designate which part of the mask is sharper than the other. It sounds like just as much work to me as creating two masks.
Among other things, variable edge feathering allows you to have gradual transitions from sharp to fully feathered, which is particularly useful for objects that are partly in focus and partly out of focus. Gradual transitions in feather-width are difficult to do using multiple masks, but trivially simple in Mocha.
Using multiple masks is good for multiple portions of an object that move independently (i.e. arms/body/head), but being able to adjust edge feathering should require multiple masks, especially when feathering is a feature that needs to be animated to match blur/focus issues.
An additional advantage of Mocha is that masks can auto-track object movement.