I don't have anything with a grip safety, so I'll reserve comment until I have had experience with them. But for magazine disconnects, I don't want or need them on my range guns , but definitely prefer them on a carry gun.
IMO, there are two main scenarios with a magazine disconnect that are important, and need to be factored into the decision of accepting a disconnect or not. I don't see it as a safety device to prevent an accidental discharge, as proper handling and training will take care of that.
One scenario is the accidental full or partial ejecting of the magazine thus rendering the firearm incapable of being fired. This is actually addressed in the normal course of training with malfunction (TRR) drills.
I also test my carry setup to be sure it's not prone to accidentally ejecting while carrying, holstering/re-holstering, or handling. Just as I do with putting lead downrange to ensure there are no jams, FTF, FTE, or other malfunctions. Once I know its not prone to accidental ejections, I don't worry abbot it. If it happens the training kicks in and resolves it in the normal course of malfunction clearing.
The other scenario is more troubling to me, that being wrestling with an attacker(s) over control of my own firearm. If they succeed, that leaves me unarmed and at a severe disadvantage. The magazine disconnect now has the option of becoming a tactical advantage . If all other possibilities fail and I can't gain the upper hand, I do know I can press the magazine eject button (if it hasn't happened already in the struggle) to make the firearm inoperable.
There are far more options now with him holding an inoperable firearm, especially if he doesn't know it's incapable of being fired. If I regain control of it, I also have the option of making it operable again with my spare magazine (or the original if I still have it).
I find it far more useful as a tactical 'feature', and less desirable as a safety device. Safety is best done with training and common sense, and not mechanical features designed to protect those that do neither of the former.
This has never made sense to me, you NEED a holster in order for a Glock to be considered safe
Its no different with a Glock than any other pistol in my opinion. Any firearm is safer in a properly designed holster to prevent anything from contacting the trigger inadvertently while carrying. I won't carry any handgun if it's not in a holster that covers the trigger guard.