This all depends on your relationship with your dealer. If you get a proper map (the likes of RS Tuning) they will map the car within Renaults safety parameters, mine is. Everything on a modern car has safety built in, if the car starts to detonate, it will retard the ignition, if the gearbox is getting too much it pings up an alarm. A good mapper works within the parameters that stop these things happening. I would recommend Paul at RS Tuning, I had a Bluefin map but it would ping the spanner on, some get it some don't. Ktec are still having some problems I think hence the general release is not available, but they may have sorted the problems now, they do have a car making 275 bhp though!!!!!!!!
As for reliability, how does an average of 35.5mpg sound, commuting and blasting. The car drives a lot nicer in auto as well, in fact 90 % of the time my car is in auto, if I want to pass something, just press the loud pedal and the car instantly downshifts to the ideal gear and changes up when it hits the redline automatically, I just hang on and go.
There are a few downsides, the extra power (230 bhp) is on the chassis's limit, with more torque steer, and the car becomes a bit on edge with the extra power, progress is rapid, B roads are a hoot, but to really exploit the extra power a suspension upgrade is the next step, I'm afraid.
As for warranty work, a good dealer wants your repeat business so will look after you.