This device will produce a negative effect for mechanicals.

Mechanical broadheads need a STRONG impact to properly force open the blades, which is derived from the momentum exchange of the initial impact (or relatively interchangeably, since both rely upon mass and velocity, Kinetic energy). For an equivalently weighted arrow, the slip hammered arrow would have LESS initial impact because the momentum/KE of the arrow body is lessened.

Consider this: Put a nail in a hard piece of lumber, and strike it twice with an 8oz hammer. The resistance of the wood will withstand both impacts, failing to penetrate. Now, strike the same nail once with a 16oz hammer. The nail will penetrate into the wood. There IS a 'critical mass' for force that must be reached in order to overcome the resistance of the flesh, just as there is a critical force limit for an arrow to open it's blades properly and penetrate skin and flesh.

Ultimately, it's a gimmick that will prey upon those that don't understand simple high school physics. These devices won't penetrate better, not even when impacting bone, and they'll result in more failures to expand for mechanical arrows.

But then again, it's common fact that bullets weigh less when they hit a deer at 1000yrds than they do at the barrel because of the wind erosion in flight, and big fish will weigh less when you get them landed if you let them fight too long because they'll burn off some weight during the fight... If you sail west too far, you'll also drop off of the edge of the world...