Im doing some research on these particular brands regarding their stacked disk laberynth design to control excesive noise and cavitation mainly in power generation applications and oil industry.
It would be quite helpful if you guys could share experiences (good or bad) when working with these brands and if they actually solved any problems you might have had.

I have specified many control valves and only one drag valve.  This was a client driven opportunity where an existing installation was breaking pipe supports etc.  Very high noise levels above 110 dB can be mechanically destructive.  As far as I am aware the drag valve fixed the problem.

Be very careful.  
Noise is one thing. (Expanding compressible gases) Cavitation prevention is something else (liquid flow).  
Both use tortuous flow paths but the differences are significant and great.  The parts do not interchange.  

These are extremely critical applications in power plants.  Not just for revenue generation, but for the potential for personal injury.  Evaluate each application with a full set of service conditions, pipe specifications, water chemistry, and incidental data such as whether there are any particles in the line and of what size (Some trims are not junk-tolerant and some are)
Most every major control-valve manufacturer has 6 or more anticavitation valves and a similar number of noise attenuation products.  Each have specific features to solve specific problems.  You definitely want to interface with a senior application engineer at the vendor while specifying these.  
Valid sources: CCI, Emerson, Masoneilan, Valtek, (In alphabetical order).

As mentioned by Jim, noise and cavitation are two different things.
1)
Noise is controlled by breaking down the energy of the pressure drop.
2)
Cavitation is controlled by avoiding that the lowest pressure in the valve (which is lower than the outlet pressure) remains above the vapour pressure.

I also think that staggered disc with a tortuous flow path is very different than a labyrinth trim were the flow from different paths collide into each other.

For noise control I have seen four different methods:
a) Tortuous flow path, with expanding flow areas.
b) Very small holes, resulting in very small yetstreams.
c) Labyrinth trims, with colliding flows.
d) Silencer box.

My experience is that all methods will reduce noise, because of power absorbtion in different steps. However not all methods are equally effective:

a) Tortuous flow path
Based on the Pressure x Volume should be equal principle. Although this works great for cavitation, this is not as clear regarding noise.
b) Small holes
Simple solution. Will shift the noise level to higher frequencies (non-audible). May cause problems with nearby ultrasonic equipment.
c) Labyrinth
3D labyrinths have the lowest noise levels at the same valve size. 2D labyrinths are about the same as the small hole principle.
d) Silencer box
Effective, but has a limited operating range. Tends to clogg in case of dirt in the gas.

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