The Sheild is available now either with or without a safety.
I just purchased a 9mm to switch off to at times from my Smith Model 36 snub. I got the model with the safety - some like them, some don't. The safety is smaller but can be "thumbed off". Mine will be carried with a round in the chamber and the safety off.
It's no different than carrying a revolver for SD with all chambers loaded - they are made (I'm talking DA "newer" revolvers) to be carried with one under the hammer as they have hammer blocks/safety designs so they can be.
The Shield still has a "safety trigger" even if it does not have a standard safety. Plus, since it's a DAO, the trigger pull is stiffer (unless mods have been made). The important thing if it's being carried for SD purposes is that the holster used fully covers the trigger area so there can be no accidental "snags".
A person is going to carry their handgun in the manner they want to. Personally, I would neve carry without a round in the chamber. Many semi-autos - and the Shield is one of them like many others - has a strong recoil spring which means that racking the slide and putting a round in - especially under stress - is not only time consuming but difficult at best. A SD situation will occur in seconds - not minutes. By the time a round is racked - it could be all over with you being the "loser".
Any pistol class I have ever taken - and I've taken quite a few taught by LE, former military spec. ops., swat team members, etc.- have and will tell you that a holstered SD handgun with an empty chamber is worthless.
You can have an accidental discharge with any handgun - Shield, Glock, Ruger, Colt or whatever and the first thing that comes to mind is the person putting his finger not he trigger when drawing . . . that's why ii is extremely important to train yourself to keep that @#$%!@ finger off the trigger until your are ready to shoot. Yes .. . a handgun could fall and hit the ground and you could have an accidental discharge under unusual conditions.
I carry on the belt and prefer a thumb break holster but that's just me. Many use kydex holsters or open top holsters, etc. and it's a personal choice. On a Shield, if I was going to use an open top holster, I'd be looking at a good "retention" holster that insured the handgun was securely held in place but would still draw easily if needed. And as with any semi-auto - a loaded spare magazine that is easily accessible is also a "must have" as far as I'm concerned - along with lots of training and practice of clearing jams and mag switch outs to "keep going" if need be.
The important thing with any handgun is to read the manual and then read it again. Shoot it, practice with it and "learn it" and all the safety features and how it functions. The Shield is an excellent choice and he won't have any problems with it as long as he practices and shoots it on a regular basis so it's "second nature". Good luck!