The augmented system (halftone slide) with its 4 patterns is not difficult to learn. You can interpret these 4 patterns as being
only 2 in some way: everything can be played vice-versa (concerning the slide and breath direction) and you have the same melody in a new key...
That makes it probably the most regular, symmetrical and most logical system (e.g. in diminished you have 3 patterns for all 12 keys. This is true if you ignore the enharmonic possibilities. Using the redundant reeds in diminished makes it more irregular).
Only press/release the slide for semitones: on an augmented tuned harmonica for any major scale you have to move the slide only twice regardless which tonality you play in. Means, not using the slide produces a holetone scale.
Easiest way of playing chromatic scales (very fast if necessary).
It is reasonable to concentrate more on the scale patterns than on "anything else than C Major = press the slide" (as often demonstrated in schools for harmonica in solotuning).
Augmented tuning is very comfortable and secure to play. Using the button is not more complicated or expending than on any other instrument (think about fingerings on piano, guitar, woodwinds etc.).
Playing legato passages is a challenge on every instrument. Specially when the line is interrupted by inevitable technical facts as plucking/"knocking" (guitar, piano, cembalo), bow changes (stringed instruments) or breath change. If range wouldn't matter I'd go for a BLOWHARMONCA or legato tuning
roady43