For my S&W 3rd Gens, its really a non-issue, if anything, I perceive it as an asset.
Unless you're shooting competition, where the rules require you to drop the mag, rack the slide, and pull the trigger to display an unloaded gun.
Those people who bemoan the magazine disconnect safety have NO real life experience or can even find any actual occurrences where a mag disconnect caused a victim to be shot, to support the benefit of no mag disconnect, despite the numerous occasions of real life occurrences where a mag disconnect has saved a life (cops as well as civilians).
While we all hope that we never have to shoot anyone in a self defense situation, if you do shoot someone, and you have removed the mag disconnect or modified your personnel defense firearm in any fashion to defeat any of the manufactures safety measures, its not going to bode well for you when you have to go to court to explain your actions.
The 5900 series handguns are great firearms. Your 5904 will perform great for self defense, just shoot it and become familiar with its operation, you will enjoy it!