Given a choice I'd go for mag disconnect but no internal lock. After some snooping, I don't think the internal lock will be a reliability issue, when the plugs for the hole become available, in goes the bung on my personal piece.
Both the magazine disconnect and the manual safety are good weapon retention features. Doesn't chain the weapon to your body, but gives you a way to deactive the weapon if you're losing control of it. Also gives precious additional time for remedial action.
Many of the positions put forward about the "dangers" of the magazine disconnect don't stand up to critical examination/history. I've watched about 2 million rounds go down range from magazine safety equipped pistols, the only failures to fire I'm aware of were due to failure to properly seat the magazine. The result was the same as the same action without the device: Bang, Click. The cure was also the same: Tap, Rack, Ready. Can't fire the round in the chamber while reloading? That's a tactical reload, done from behind cover, during a lull in any action and with the fresh mag right beside the weapon. Where's the threat?