Interesting upgrade. Most effective in a high FPS setup. High ROF setups (Like mine) makes so much motor noise that it really doesn't matter what piston head you have on, the piston won't hit hard enough to make it worth the work. However, on a high FPS gun, the piston noise can be quite prominent at range, making this a worthwhile investment if you are going for stealth.
When it comes to installing this, you need to make sure you have the right piston. This will mess with your AoE since this head is still thicker than a standard head when the bubble is depressed (which is so stiff, you cannot push it in by hand, which is actually a good thing). Because of the extra thickness, you will probably need that 2nd tooth that normally gets sanded out on the piston. Instead, you will probably be better of sanding the 3rd tooth instead (if you can make the AoE work without sanding the 3rd tooth, props to you). The sector gear will catch it by the 2nd tooth instead of the 1st stop on the piston, which does cause a possible grind issue, since the last tooth on the piston will end up getting hit by the last tooth on the sector gear. This is because the 2nd to last tooth on the sector gear will release the piston altogether, but the last tooth on the sector gear ends up hitting that last tooth on the piston as the spring is decompressing. A fix would involve removing a tooth from either the piston or the sector gear, if you're up to grinding down some metal.
I personally put this in a high speed P90 on a G&P M120 high speed motor on a 9.6v running through deans. When I first intalled it, the heavy spring I originally had destroyed both ends of my old piston (the one metal tooth and the back stop cracked clean off), so I just put in a lighter spring after replacing the piston and grinding the third tooth. I recommend that only those experienced with high performance gearboxes install this part, as there is a high chance you will need to grind some stuff down to utilize this piston head correctly.
I give this a 5/5 because of the face this basically eliminated all piston noise in my gun. The motor just happens to be the only thing you really hear, which would be a problem in my case, but on a ~400 FPS DMR at distance on semi, this will nearly silence your piston.
Nearly silences the piston
Bearings are always nice to have
O-ring provides a great seal
Not very expensive at all
Requires major adjustments be made, causing for a lengthy and difficult installation
Messes with the AoE more than some would like (may cause a slight FPS drop)