I love TipGenius!
Our store is called Pink Horseshoe (you can see an example of this app at pinkhorseshoe.org) and we are a new women's clothing brand. We are very unique because all of our profits from our store actually go to charity. So we actually use this app as a way to add an extra donation to our charity!
The support at TipGenius is amazing. We wanted to be able to edit more of the text on the pop-up and within one day they updated their app with this new feature! Incredible service. Love the app. Great way to get tips or donations on your website.