Den,

Fret buzz should not necessarily be a characteristic of the octave mandolin (octave mandola here in Europe). I have no fret buzz on mine (admittedly high-level instrument as it is my main one but which is fairly heavily strung in unison and which has a fairly low action). A good setup combined with the right stringing should virtually eliminate buzz, even on a more budget instrument.

Peace,

moo

P.S. I don't know the Johnson but have played several TCs which seemed fairly good value instruments.