I have just moved on from the Nike Method to the Versa level 96, but I was most reluctant to do so, the Nike is wonderful.
As for scale, anything over 14 feet I used the 50 scale, the 10 only for putts under 5 feet. and all else the 20, as most of my putts are under 20 feet.
The 10 scale requires a little more power than normal, e.g. 5 foot putt on fast greens hit six.
You'll get better results moving the aim marker, on a breaking putt, and also miss the ding fractionally on the high side.
Hope this helps
1i refreshingly imperfect