Subtotal works the same way as United MileagePlus X. When you get your bill, you buy an instant gift card through the Subtotal App for the exact amount of the bill. The server can scan it, or you can use the tabletop Ziosk for those restaurants that offer them. If you don't want to hand over your phone, just give them the gift card number that comes with the bar code. You can also include the tip in the GC if you want.
No independent restaurants, but almost every chain you can think of is a partner and you'll get a rebate to your credit card of 1-10%. It's super-easy. Even I was able to do it.
Get $1 for each referral.
https://subtot.al/refer/38SZ
Mike