Nice. I also have a nice mic and mic stand to do detailed measurements from the listening spot (Earthworks M23 calibrated mic), but I would recommend that you still to the phone measuring on top of the calibrated mic measurements with REW. Here's why - the calibrated mic will give you excellent results from a single listening spot. But, the phone app will let you go mobile. So you can measure as you walk around the room, which lets you get real time measures of different locations in a very fluid way.
Granted, it's not 'perfect' measures like the calibrated mic with REW gives you, but you don't need perfect for this. The phone will let you see where the most egregious areas are, as well as were the best areas are.
Tyson do you have a good link for a basic walk thru of how to perform REW? Everytime I search its sales data, the theory behind it or LONG videos/webpages about the process. I've not yet seen a "quick start" guide.
thanks