Russ - I expect that the agreement (closed source) with Plasmerg would also prevent you from selling the kit on. Since you haven't signed the agreement, though, it probably is not legally binding (best check with the lawyers among us). The likelihood of getting your money back from them, however, seems slight. Personally I think it can't work in its current form and would thus be a bad investment, but the people who might bid for it will of course know that so you would not be selling it under false pretence.
On Axil's problem of mixing of the gases, look at the way dust is suspended in air. A dust speck is a lot heavier than a molecule of Oxygen or Nitrogen, yet still floats. Layering should not be a major problem if the gas mix bottle is shaken before use, and once in the popper the gases will be mixed by the first pop and should remain well-mixed for at least a minute or two before the heaviest starts to noticeably settle out.
On Axil's problem of mixing of the gases, look at the way dust is suspended in air. A dust speck is a lot heavier than a molecule of Oxygen or Nitrogen, yet still floats. Layering should not be a major problem if the gas mix bottle is shaken before use, and once in the popper the gases will be mixed by the first pop and should remain well-mixed for at least a minute or two before the heaviest starts to noticeably settle out.