I have on both accounts. The dampener is not necessary and I don’t recommend for brake pedal specifically. I have mine on my gas with a bit more than 1/4 of the available dampening force to allow for smoother gas pedal usage. It has helped on turn exits and standing grid starts.
For the brake the performance kit is a must:
The human body memorizes muscle tension much better than foot position. This is why all car brakes measure the pressure and not the travel. Race and F1 cars have almost no travel at all.
The difference is night and day, and the better you get at braking the harder you end up preferring the load cell brakes. It allows for more precise control. The dampener on brakes adds a delay to the brake pedal springing back to its 0 position so it seems to hinder the brakes in my opinion as opposed to enhancing as it does to the gas pedal.
The Clubsport V3 pedals feel heavy duty and closer to real pedals. It needs to be bolted to a rig since it has a load cell brake. The ones that came with the GT DD Pro feel more like fake pedals in comparison even though they are sturdy and solid in their own right.
Also the Clubsport V3 Pedals also have more travel (edit: I mean more articulation, not travel. Brake can be set to minimum travel distance) so they are far more precise in controlling the amount of braking and gas as opposed to the others that kind of feel like more of an on/off switch by comparison.
They also are configurable and you can change the travel distance and springs for hardness.
Bonus: if you play ACC the rumble motors on the Clubsport V3 pedals are compatible with the game and work.