U-value of windows: 1.3 - is an upgrade worth it?

Sorry, mushroom head locking doesn't prevent break-ins, it only makes them about 10 seconds longer. In that respect: I would avoid retrofitting and gradually replace the windows.
Additionally, the values of the windows must match the house insulation, simply installing xy across the board doesn't make much sense.

Best regards in brief

makes it about 10 seconds more tedious

Source? Because I think that is simply wrong.

Source? Because I simply think that's wrong.

What do you mean? 20?
We still have drilling and welding the window in our repertoire...

Regards, Yvonne

RC2N has a resistance time of 3 minutes according to EN.

What do you mean? 20?
We also have drilling and burning open the window in our repertoire...

Best regards, Yvonne

I'm talking about breaking in, you're talking about prying.
By the way, during retrofitting, probably only as many locks can be added as are already there. But I'm not familiar with that.
My source, by the way, is my experience from my profession, which is called Spusi. You don't just swing the brush there ;)

Best regards, Yvonne

But you know better than us that the majority of 08/15 burglaries are done with screwdrivers. You are talking here about semi-pro to pro, and that occurs rather rarely.