are u talking about hasbro/takaratomy toys or the new dual model kit? If the normal hasbro toys, its better to separate them if u're painting with airbrush. But amateur like me just brush paint on it without separating

take it apart and u can paint it better / easier to reach those tiny / slim edges between parts n all..

if u use airbrush, of course will need masking, u wouldnt want to spray over things u dont want to...rite ?
if painting it manually, make sure u have steady hands, abit hard if u have "shaky" hands..