We used the APP for the Phase 1 on our Dream Tundra last year, and it worked out well for data gathering missions. Airplanes that meet the requirements are pretty well known quantities, having been built to plans, with engines recommended by the manufacturer, from established kits. Yet I am still not comfortable putting two people in an airplane for a first flight because even trivial changes have gotcha's that might not reveal themselves until you're airborne. Other's disagree with this, and the APP does allow first flights with two onboard - you'll have to make your own risk decision, and you have the freedom to do that.
It turned out that our partner in the Tundra, the man who started the project eight year's earlier, did not meet the insurance requirements to fly it as PIC, so the APP gave him a chance to be a part of the program once I was happy that we'd accumulated enough hours that the potential "big surprises" were past. We did run in to some interesting issues in checking out a local instructor who was also going to be a part of the program, because the insurance required that he have five solo hours before he could take anyone else up, but he didn't meet the requirements as QP. No problem, I figured, I'd be QP for his checkout flight - but since he had no financial stake in the airplane, he didn't qualify as BP! A funny little loophole that made him do his first flight solo. How does THAT contribute to safety? (I wasn't worried, he owns a similar spam can, and has plenty of time.)
Read the APP very, very carefully, use all of the worksheets, and make sure that you have all the i's dotted and T's crossed, in case something happens. It is easy to acccidently color outside the lines. There is paperwork to be done, and logs to be filled out - ground tests that must be documented. Then take advantage of it to fly safely - or at least with lower risk.
Paul