Hi Ingo,
if you like it - then it is really perfect 
I love the heel kick shifting method very much, there’s a bit training required, but once you got it you can shift upwards during pedaling. 
Btw, your ATS drive might be happy to receive a few ml of grease once or twice per year.
Also, neither ATS nor Schlumpf drives are 100% sealed, small amounts of oil/grease next to the drive’s gaps are normal. Regarding information about speed drives I’d highly recommend the original Schlumpf drive manuals:
http://www.schlumpfdrive.com/index.php/technical-documents-254.html
Chris