I have only flown on Empty Legs but they don't have shuttles in Europe yet. If I were to book a charter (which is doubtful, those are much more expensive), I would want to do more research as to the price comparison, since JetSmarter is basically a broker and does not operate planes themselves.

By the way, the empty leg that I flew yesterday was the best yet. A legacy 650. I had the entire plane to myself, along with my own personal flight attendant. Too bad it wasn't a very long flight.