The only reason to use a piston spacer over sorbothane is if you're running a high ROF build, and sorbothanes recovery time ruins AOE in full auto, so you're required to correct AOE by adding spacers to the piston head instead. This unfortunately adds a pretty substantial amount of weight to the piston usually, as we often use aluminum/steel faucet washers to accomplish this.
This product was supposed to only marginally increase piston assembly weight and provide a small amount of damping, which is great for high ROF builds.
However.. within 10,000 rounds of adding this to my piston it completely shattered. This created space between the piston head and piston which ended up causing catastrophic damage to my Retro Arms piston, FPS piston head, and siegetek sector gear in the middle of a game. I was only running an SP150 on an 8 tooth DSG, so I don't understand how this happened.
Given that this likely would not have happened on a full stroke M100, I still don't see how this product is useful because in that case you'd simply opt for sorbothane instead.
Link to image of shattered spacers: https://cdn.discordapp.com/attachments/369981816196562945/1213264834418704475/IMG_4181.jpg?ex=65f4d7ed&is=65e262ed&hm=3ed295a7b1fadbe502e8eb16d7a79f0eb2a730e5a30a3d1e984d70aaacdfef26&