Not similar to the Payne Stewart accident in that Stewart's Lear flew thousands of miles at FL320 (assumingly trimmed and on autopilot) before exhausting fuel and auguring in. If this was hypoxia and they all simply passed out and died wouldn't this aircraft have maintained it's heading at FL280 overflying Toluca and beyond. The early reports of this accident seem dubious.
Final demo flight, my eye. Coming from an operator with a long and well-established history of flaunting regulations, I do not believe this for a second. When will someone finally grow a pair and crack down on "demo flights" used to disguise illegal charters?
I say you should only get ONE demo flight. If you want more than one, be prepared to show the FAA you've put down earnest money and have a pending purchase contract. Otherwise it's people taking advantage of a loophole and avoiding legitimate 135 operations.