As Sean has said we have them on 4 of our games at Schwoegler's. I dont personally have a smart phone so I wont ever get to use it, but so far it seems many people like the idea and dont carry cash so it is a convienence for them.
From my perspective, the #1 call for any game is the coin slots are not taking money. Payrange provides a was to play even if the coin slot is jammed.
Side benefit is less dealing with dirty coins and hassle of counting and rolling.
At $50 a game I find it a bit pricey (esp since they already take a cut off each credit), but it will be a nice experiement to see how much it is used.