Jigeye,
The other difference with the Q series is that it's a larger sized muffler. I just finished reviewing the Great Planes Cherokee for RCU and I originally was going to use the Q series muffler. But when it was mounted the size of the muffler interfered with the nose gear steering arm, so I couldn't use it. Instead I used a compact Pitts from Slimline.

Other than those considerations, there's really not much difference between the two muffler brands. I have used both many times and they both perform well.

Ken