Stack-on makes a decent, low-cost 'gun cabinet', but no way I would call them safes. I mean the hinges are on the outside for pity's sake.
PowerFactor did a safe 'walk-through' that was pretty interesting...
http://www.powerfactorshow.com/2013/07/08/episode-133-tour-of-nwsafe-part-one/
They show a lot about why cheap safes may look good but don't really work.
Hinges on the outside are fine, as long as the door has some type of fixture (typically dead bolts) on the interior hinge side and doesn't rely solely on the hinges to keep the door secure to the frame. Even the entry level safes with external hinges are built to not rely on them for keeping the door secured.