alot of the mufflers now have grooves on them, so when a extension is secured to the pipe end its not going to slip off,last weekend I crashed one of my planes with a OS 46AX the extension was still firmly secured to the pipe, evn though the prop,and spinner, was busted, and the engine was covered in dirt.

only time I have had trouble with them staying put was with the muffler that has a smooth end with no ridges then there isn't any thing to grab firmly on to, a ridge of JB Weld on the end would have been handy to hold the diverter on in that case.

if you tighten the tie wraps down and give it a bit of a tug and it doesn't come off then it's going to stay put.

how does one compute 15% loss in power,this will probably start another round of debate of course.

I havent lost any exessive amount of power from having a deflector on the muffler, seems like some engines are more sensitive to a 1 1/4" piece of tubing, I use them on 2 and 4stroke engines