They are great, and very handy especially for MD rockets. I use Mayhem's on my Go Devil 38, only had three issues in around a dozen flights, first time I'm pretty sure I did everything right yet the guide failed to come off, rode the rocket to apogee, shortened the flight quite a bit from its expected altitude and the guide was lost. Once it came off as expected but broke when it hit the ground. Third time was totally operator error, it again rode the rocket to apogee, but I realized afterwards that I hadn't even looped the rubber band over the clips, so there was no way it was going to spring open.
Always ensure the guide pops open on its own before the final clamp around the rocket and feed onto the rail.
Besides the fragility (they come off quickly, but can still end up falling a decent distance, onto potentially hard ground), the fact that there are 3 buttons can sometimes make the fit onto the rail difficult, there was a time that I simply couldn't get it on the 1010 rail and had to move to a different pad. Another time I think the rail channel was a bit wider than usual, and I couldn't get the guide to make a tight-enough grip on the rocket to stay in place (even with an extra rubber band wrapped around each side to make the diameter smaller), had to go back to camp and grab more rubber bands to build it up even more.
I'm building a RW Double Shot (2-stage), and for the sustainer which I want to do a test-flight on its own first to verify the electronics I'll use a 54mm Mayhem set, to avoid having to punch any temporary holes in the airframe.
