KennyRoy,

The Mac's one-piece costs $34 at Tower and adds no power.
If you de-baffle and drill the stock 783 silencer, you will get just as much power gain as drilling the Mac's, without wasting a dime.

The only advantages of the Mac's one piece are its size and weight.

Using even a rudimentary tuned system, like the Tower/Hobbico .46 muffler ($15) will give you much more power than you will save, with the light Mac's; about 400-1,000 RPM.

If you want a lot more power, the very expensive Jettstream and Ultrathrust are only $20-$25 more than the no-gain Mac's.