WITW is a Z-Valve

[CoFFeY[NiTrO]]

What in the world is a Z-Valve?
here is what a website says...

Change the Automag into a low pressure, 'Reactive' trigger, Tournament level machine. This On/Off Valve and Reg Pin replaces the old parts. Just by replacing the parts, the velocity will increase, thus allowing it to work at lower pressure making it more consistent and gas efficient. The trigger pull is shortened and has a reactive style like the RT series from Airgun Designs.

Is this another Automag "No No"

[Thordic]

Its pretty much useless, and it cant truly emulate the Retro valve trigger feel.

Id say its a waste of money.

[PyRo]

Yes, this is a no-no. It causes problems including increased wear, leaks, and just plain messing up your gun.
The on/off in no way has any effect on your pressure. It has no effect on the consistancy or gas efficiancy. All of that is just a big lie.
I think it does make your trigger pull slightly reactive, but not as much as the rt, but you will incur the above problems.