Most of the modern ones are built for mobile first since that is where all the fans are. I've never had an issue fueling from my iPhone while I'm at the game or watching at a bar. It’s usually just a couple of taps. RallyFuel is actually really smooth on mobile browsers. You can try it yourself, just go to https://rallyfuel.com/athletes/brandon-klatsky on your phone. It loads fast and the payment buttons are easy to hit. No desktop needed.