They are good, I flew on some rare airplane types a few times in the last two years. It are airplane enthousiasts like us, professionally organized, friendly and reliable, no hidden tricks or scams. The only risk is when the flight is cancelled they will not be liable for any financial damage you got to get there, but that's only logical, only this way they can keep their overhead and prices acceptible. They had a Li-2 flight cancelled due to bad weather and later the overambitious Boeing 720 flight also didn't materialize.
nobody has ever died from hard work, but why take the risk?