As Gunsnrovers says, some people dislike the plastic safety button. Personally, I haven't had a problem with mine. Midway USA sells a metal button, and installing it isn't hard but you have to mind the small parts (specifically the detent ball and spring, they're TINY).
Some 'smiths I've talked to said the plastic button was a move to prevent damage to the action if you whack it really hard. Plastic breaks while metal transmits full force to the trigger/hammer assembly. I have not had experience with severe trauma to a Mossy, so I can't tell you firsthand if it's true.