Hi David,
Measurement process seemed similar to me probably because I have spent way too much time with REW over the years and am very familiar with it. It’s true that I had already taken successful measurements with Impala this morning within 10 minutes of installing it whereas with REW there was a long learning curve.
I checked the REW manual you have shared. You are aligning impulse peaks rather than IR starts which is exactly how I do it in REW. But I was more interested in the transfer function applied final average measurement produced in FF to which you base your correction 
I agree that a working demo would be hackable, would have already produced the wav files needed and eventually would ruin the business and I also believe the price is quite reasonable for something that really works. May be, you should consider convolving a demo song with FF filters for users based on their measurements and send them to hear the potential results.
Btw, @Markus_Hubner has posted this info under this guide discussion which has been replaced with my new method some time ago which is here:
In this method, I am inverting the response over a Harman curve and generating minimum phase FIR filters all in REW. It’s quite efficient and people are consistently getting good results with it so far but there’s space for improvement in group delay and phase alignment in the bass area. My attempts to further develop it by time reversing excess phase below 500Hz have consistently failed with massive pre-echo effects. So in fact, just to learn how you guys do it, I would be willing to cough $250 and probably will one of these days 