its rare the aux tensioner lasts past 3-4 years before it becomes noisy from my experience, and due to the crap design of it the belt does get worn (have a look, you'll see a nice line down the middle of the belt)
the aux kit isnt expensive and its a simple 1 hour job to replace it
"according to the book" - yeah but this is renault, they reckon you only need to change the oil every 12K, (on all RS cars) yet i do 2 dephaser pulleys a week which is caused by lack of oil changes, F4R engines are every 6K without fail
yes the cambelt is due at 5years, but if you have the aux kit replaced at 3 years whats the big deal? it can be replace seperate to the cambelt and doesnt neccesarily HAVE to be done with cambelt