Decocker is safe--using your thumb is less safe
I am firmly on the side of using a decocker. It is MUCH EASIER to have an accidental discharge while lowering the hammer than by using a decocker. I much prefer the decocker on my SIG'S to the hammer dropping safety on my WALTHER PPK.
With the SIG, I press the lever and the gun is safe, but still ready to use.
With my WALTHER PPK, I have to press the safety down and then remember to press it up again. An extra action and one which if forgotten, renders the pistol useless.
I have been carrying both a SIG 232 and WALTHER PPK for several years. In checking the PPK before carrying it, I found that I left the safety on once. Only once is not too bad, but if I had missed it, it could have been tragic.
I have a CZ83 and it is a good pistol, but the lack of a hammer dropping safety makes me rule it out as a carry gun. I would not even consider it for a new shooter.
Sure, I can just lower the hammer, but the less experience the user has, the more likely they are to make a mistake. WHY INCREASE THE RISK?
Please note, I cannot think of ANY LAW ENFORCEMENT AGENCY THAT ADVOCATES JUST LOWERING THE HAMMER AS A STANDARD PROCEDURE for their general issue weapons (FORGET ABOUT SWAT or ENTRY TEAMS, this is not about them).
Jim