Thanks for sharing
The slack, do you mean it has yaw on the connection to the stock? (look at an airplane pitch, roll and yaw if that didn't make sense).
One negative I see is that it makes your stock forearm another what 1/2" to 3/4" higher? But that is probably not a problem for most shooters. And what does it weigh?
Spozed to use white chalk to outline your foam cuts.