Both are very useful, somehow I actually prefer the setup on the Scheppach because the setup/calibration is simpler. A company called Machine DRO stock them in the UK http://www.machine-dro.co.uk
I wouldn't want to be without mine now. I usually find myself machining quite a range of sections for a particular job (mainly aircraft wood rather than furniture these days) and they transform the speed at which you can get exactly the size you want and it's great just being able to dial in the thickness you need and get accuracy to a few thou.
I've got a wixey one on my startrite SD320 and it was easy to fit. I can take some photos tomorrow if you'd like. There was also an article in one of the ww mags not that long ago on fitting one - I'll see if I can find it.