Don,
I've used Superfil for many years on two different airplanes.  It's actually superior to using micro since the hardness is consistent batch to batch and can to can and micro is not.  It's a world easier to sand and doesn't create cratering problems you get with inconsistent hardness.  It's epoxy base so it's robust.  You will need a gram scale however to mix it.  It's a 2:1 mix and one normally uses small batches since the working time is about 30 minutes depending on temps.  The best way to mix the Superfil is to spoon out a qty of part A into your cup sitting on the scale.  Multiply this by 2, add it to the part A gram weight and spoon in part B until that total is reached.  I bought a kitchen scale accurate to .5 gram and it has served me well.  I do, however, hardily recommend NOT using Polyfiber primer.  It's bad stuff.  It's hygroscopic and will start absorbing moisture from the day it dries.  I had to strip my Q2 down to the glass and totally refinish it since the Polyfiber primer had started to fleck off by the time I was ready to paint.  I've used WLS on the Legacy and it really is good primer.

Gene
LFG