My PPQ trigger breaks right at five pounds. It breaks in the same exact place every time consistently. My glocks have the mush triggers that feels much heavier and inconsistent, but break at just over five pounds on the gauge... The gauge doesn't lie. I reckon my PPQ is as safe as any Glock out there, and has roughly the same force requirement to pull the trigger. The PPQ's trigger just works more like a trigger ought to.
To the OP, whether or not it is safe depends on the shooter. Whether or not you are comfortable with carrying a pistol with this trigger depends on your preference in triggers and your own comfort level.
There are people out there that don't feel comfortable carrying Glocks either, so if you don't feel safe with a trigger that short or light, you are not alone. If this is the case, don't carry it. Make your own choice.
Personally, I have no issue with my PPQ's trigger, and I carry it every day.
That being said, I would sure dig a manual safety on the walther... (Hint for our German friends that make these excellent firearms)
Walther has been a DA/SA pistol manufacturer since they invented this trigger action over 80 years ago on the Walther PP. Someone correct me if I'm wrong, but every model of defensive pistol that Walther has released since 1929 was designed around the DA/SA trigger action.
I believe the PPQ is the first model of defensive pistol from Walther to not have a DA/SA trigger variant since 1929. It seems that they are trying something new for the American market, and them setting up shop here in the US tells me that they are starting to show more interest here, but I don't know if we will see a cocked and locked Walther (or a .45, or a .357Sig) just yet, if ever.
I prefer cocked and locked pistols.