Currently only the Raspberry Pi 3 is supported. I'll look at adding support for other devices over the coming days.

I was wondering about the kiosk itself.

I'm not sure I understand your question in that case. I do mean the kiosk itself.

You might have multiple Raspberry Pis (one for each screen) and then they just connect to tellybox.me to provide them with their slides.

Changes can be pushed to the screen by editing the slides on tellybox.me and hitting the refresh button on the devices page.

I think I understand, now that the customer already needs to have kiosk hardware like screens, an enclosure, etc. and the product is software only. Right?

That's right. If you've got a TV and a Raspberry Pi your ready to go :)