Perhaps I'm missing something here. What would be the drawback of installing the Crytopay swiper with the button on the vacuum? What is the advantage of installing the swiper without the button on the vacuum?
It depends on how you want it configured. You probably aren't going to go count-up, so you don't need the swiper with the button to cancel the time, and count-up doesn't work right with combo vacs that have different times for functions. On combo units you can have it set so they can swipe their card once for a start-up credit and use the button to add coin credits, or have a swiper with no button and they just have to swipe to start and swipe again if they need more time. I say go with the button swiper, you can disable it in the setup if you decide you don't need it, and the cost is the same.
With button for sure. I just have mine disabled, but works perfectly when I need to use it in one of my bays if I have to send one of those for service. I tried having the button active and used to add time, but people would push it to stop the vac instead and end up with $10 charges. Can't fix stupid, so disabled is better and they can swipe again and pay for another cycle if needed.