I didin't know this project, but as I see it has much in common with gambling.
Will the jar owner display the capacity of the jar in advance or is it unknown for the customer what is the remaining amount before it breaks?
The customers will see the Jar's capacity expressed in USD and in percentage. It will be visible at Jar's subpage. The Jar owner can request for a change, but the new capacity will come into existence when the new Jar is created.
Example
Anna's Cafe sets up a Jar with capacity equal to 25 USD. Anna wants to give away 10 coffees to first customers. Assuming the bitcoin price is 100 USD and someone sends 0.1 BTC to the Jar --> the Jar is filled up in 40%. We will add this function - remaining bitcoins amount will be visible at the Jar's subpage.
Also It may be good that there is a 1st, a 2nd and a 3rd prize provided by the business owner if he/she want to...
Of course. It's a nice idea. Business owners may set up their own rules but they have to describe them at the Jar's subpage. But for now, in our opinion it's easier to understand this project when everyone receives the same reward.
Marek