Just because the decocker can be engaged (left down) as a "safety," doesn't mean it has to be left down as a safety. It can be in the ready to go position all of the time.
For 20 years I carried a traditional decocker/safety equipped pitstol. The first was a Beretta 92F (slide mount decocker) and the second was a 4566. In each case, the Department that I worked for did not carry the weapons with the decocker engaged as a safety. It was always ready to fire with simply a trigger pull.
However, having a decocker-only model will take away your ability to engage a safety if you8 choose. Conversely, the traditional setup with the safety ability will allow you to use it if you choose. Why take that ability away from yourself with the decocker-only model?
Personally, I find the "safety" function in both the Beretta and Smith thrid generation pistols very poor. The engagement, or ability to disengage them, takes little effort - too little effort in my opinion. Since I didn't use them as safeties, I didn't care, but if I were to use them I would expect more effort to disengage them to remain an effective safety.
They also worked the wrong way, at least from a 1911 perspective. I was used to down to fire and up for safe. On the Beretta and S&W, it was the opposite. It was a different Battery of Arms.
After all of that, if it were me and in spite of the low effort to disengage the decocker when it's used as a safety, I would still get one with that ability. It would leave me with the ability to use or carry it with or without it engaged whereas the decocker-only model takes it away any options.
It also leaves me the ability to engage it if I were in a position where I was fighting over the weapon. Should the bad guy succeed in getting the pistol from me, I could engage the safety as my last act. It might just give me an extra second to two to go to Plan B before the bad guy figures out why the pistol isn't working. Why take that ability away from yourself with a decocker-only model?
The same benefit can be applied to the magazine disconnect that many people dislike. Dropping a magainze as you last act before the pistol is taken from you in a fight could provide a benefit.
So, that's my take.