I've been watching Armadillo (
http://www.armadilloaerospace.com) for a few years. They have pretty short turn-around between tests, but the engines are very loud and hot. They never seemed to have as much trouble with the software but have invested a lot of effort in the engines. I don't know how much data you can collect from a 6 second flight, but the ability to do it 9 or 10 times a day is attractive. Combine that frequency with a safe propellant that's basically free. Maybe NASA can buy one of Carmack's vehicles when they're ready for a live test.