i think the key to using an e-file to cut the line is to have a steady hand with steady pressure ....... and training when you buy the machine of course.
I use a long medium barrel for mine, as you can cover the whole free-edge at the same time, 2 week bits don't make much sense , as usually you take of the majority of the free-edge (which is more than 2 weeks growth)
There are quite a vids around giving demos , Vicky Peters, Young Nails, there's one on my site also
Nail Zoo Video Page
But you can't beat a 1 to 1, to really understand how to do it.
The most amazing thing I have ever seen was Trang taking out the free-edge, it take him 2 secs and one movement to take the whole thing off, it was so quick, so efficient, but almost frightening to watch the speed.
In fact he was so quick, he did 2 models (in the same section) in a nail comp I judged