I say get the WE or if you can the Socom Gear one, same gun just rebranded but the WE's generally dont have trades and have a giant WE emblem somewhere on the gun. The socom gear ones have trades (well socom gear trades) and dont have stupid WE emblems anywhere but have cool socom gear ones. And they have really cool paint apps/styles on their M9's. Also most WE/Socom Gears come with a threaded barrel adapter for the barrel which you can screw off if you dont want threads on it.
And if no thread adapter is provided airsoftparts.ca sells this usefull piece comes with extras too.
Both KJ and WE are TM compatible so parts are plentiful for them if anything breaks (KJ I know is WE was last time I checked atleast)
As for the safety switch falling off, the right side is only held on by a tiny grub screw and will get loose after awhile due to the vibration of the blow back all I can tell you is locktite is your friend there.