Tablet is the general term for iPAD and other touchscreen devices of this type; if you buy an iPAD or an android-based tablet, only some standard software is installed, nothing music-specific. For the iPAD you can download "Set list maker", which allows you to operate the Ketron as I described. But for other tablets I don't know if a comparable app exists. I found an app for android tablets called 'set list creator', but it doesn't appear to have midi functionality, which you would need for the Ketron.
If you thought about the Roland SD-50, check the prices for used SonicCells, too! The SonicCell offers much more than the SD-50, you can supplement it with 2 SRX boards (which is of course not cheap either, but it's a valuable option).