Crab has it spot on. Nothing wrong with the fenestron per say( only ever used on a 341/2) The issue is the student, until he learns to anticipate and you can only do that by reaction until the eye/hand / foot coordination kicks in and you can anticipate. This means the instructor really needs to be on the ball to ensure the student is " leading " with the pedal.
Lets be honest all helicopters have there foibles
R22 lots of
S300 not many
B206 slow to react tail rotor
MD 500 massive pedal movements and heavy controls
AS 350 , nose appears pressed against the windscreen
MD520 you think a fenstron is slow to react just wait and have a go with one of these girls
SA341 exciting doing spot turns in a very strong wind
Just to name a few
I think the article seems ok, just pointing out the obvious