I am basically the opposite of a crypto expert. However, I do know enough about cryptography in general to know that this basically can't work. There is no way that I would trust a stranger, who had just handed me a piece of paper with a QR code on it, unless I could verify the QR code. In fact, it wouldn't even be enough to verify the QR code. I would want to move the funds into my own wallet first. After all, the stranger could easily have an accomplice that withdrew the money the second that I verified that the funds existed.
The note generator is an interesting idea, in that you can have a QR code that verified the existence of the funds, but you could cover up the secret with a scratch off covering. However, the person receiving the note would still have to trust the person creating the note to not have recorded the secret elsewhere. You could never trust such a note to actually be worth what it said on the front.
About a month ago I spent a week in Peru. For the first time in a couple of decades I used cash as a primary means of transacting business. I purchased things both with Peruvian soles and USD. Both of these currencies worked because the notes that were passed around were sufficiently well done that they passed as genuine. It is very possible that I handled some forged bills, but the bills were all good enough that they spent fine all the same. I did have one $10 bill, however, that was worn enough that no one would take it from me. Heck, I tried to give it away to the uber driver that drove me to the airport (I had already tipped him in the app). He wasn't interested because he knew that he would have trouble spending it.
Personally, I don't blame the uber driver. I wouldn't have been interested either. Nor would I be interested if someone tried to pay me in Amazon Gift cards or some other form of payment where the value can easily be manipulated. Unless I knew the person well, I would immediately assume that I was being scammed.