After reading through the posts, I have decided to share my two cents.

I have been into this topic for quite a while, because I find gaming with a PC-keyboard extremely annoying.

I make a general distinction between hardware solutions (i.e. button boxes, or switch panels) and software solution (i.e. software based keypads, displayed on any touchscreen device)

I find physical buttons give the best feel, but they are a bit unflexible. I'd only go through the effort of designing one, once I have established exactly what I want, and how I want it set up. For that to happen, a software solution is ideal. And of course, there's the issue of cost.

When it comes to touch screen devices, one can either use an some wireless touch device, running iOS or Android, or one can use a touchscreen monitor.

So far I have worked with the following products for iOS:

Comments so far:
Latency is not an issue for any of the iOS apps. All work virtually instantaneous.

LEA I find a pure pain in the butt to set up, with a steep learning curve. It might be really nice, once SC allows extraction of game data, and use the pad as a truely interactive device. Until then, I find LEA to be overkill, and too much of a hassle to further bother with.

CCP is Ok, but it didn't really rock my boat

Action Pad is also ok, but it seems to lack the possibility to create multiple layers, to manage a menu system. I have asked for clarification regarding this point, but have not heard from the dev in weeks.

Quadro results look nice out of the box, and without much effort. Quadro can be used to create an additional layer of depth per button. It seems, that for more intricate functions, coding is required. Also there are limitations concerning the looks of the buttons. Basically, you are stuck, which what the software has in its library. The definite pro is, that it is easy to work with, and can be set up on the fly.

CustomKeypad is similar in ease of use as Quadro, but offers some more versatility and flexibility, when it comes to aestetics. Also, the possibility to set up a layered menu system are not limited to one layer - there can be lots more. It is for the time being my prefered iOS app for the job.

However, there is another possibility. I have also attached a 10" touchscreen monitor, and installed Keyboard Designer (http://www.virtual-keyboard.com/) on the PC. In combination, TS-LCD and the runtime keyboard are a pretty neat package. There are only a few limtations when it comes to looks, it is very flexible, easy to set up, can run macros and is VBS codeable. Creating a working setup is less "easy" than with Quadro or CustomKeypad - though not really challenging. The result, however, is much more pleasing.

Latency is obviously no issue at all, as it is hard wired to the pc. Con might be, that it takes some GPU performance. I am running a 4790k/32GRam and a R9 390 (all at standard clock speed), and SC on full details does not strain the system at all. So for me, this is the best solution out of the lot...until I manage to design and build a custom button box.