I'm surprised this useless gimmick is still on the market, but I guess later generations still refuse to learn from earlier and buy stuff for no reason.
This is just another way to take your money. Many of us wasted our money so there's no reason to waste yours.
Best accuracy is obtained with all the rifle parts in the same position for every shot. A little bit of receiver wobble is taken out simply holding the gun to your shoulder. All the parts end up in the same place no matter how tight or loose you grip and hold the gun to your shoulder. Sticking a piece of rubber or an ear plug in between the receivers requires you to hold the gun with the same pressure every time. Otherwise parts will be in one place one time and another place the other.
This is absolutely a very minor detriment to accuracy but the device should be named the Inaccu-Wedge.
-- Chuck