The drop away rests that are already being produced, such as the QAD Drop Away Rest Brackets have all been modified numerous times since their inception.
The key is getting the rest properly positioned in the bracket so that the rest is exactly centered to the crossbows center shot alignment, both vertically and horizontally.
Also, the better rests insure the arrow holder stays down and out of the way after the release of the shot. This eliminates timing concerns with the arrow holder bouncing back up into the arrow shaft before the arrow can clear the crossbow.
The only addition I would like to see added to the current QAD Bracket for the TAC15
/ 15i are some etched scales where the hex bolts lock the bracket to the front of the crossbows stock and between the two halves of the bracket itself.