the biggest things that people overlook when going to non - franchised car repairers/service points is warranty and goodwill.

for you to have the vehicle serviced away from the dealer network, it is your choice, should you need to use the manufacturers warranty system (and its a renault so you will), then the owness is on you to prove that the servicing has been in accordance with manufacturer specifications.

Also, whilst your in at your non franchised service point, will they carry out any non notifying in service reworks to your renault?

and, after your warranty has expired and something then expires on your vehicle through no fault of your own e.g. gearbox failure, would you then like Renault to contribute ? maybe even a FOC repair out of warranty ?
Should your service history even have one non franchised visit then you will get no goodwill whatsoever, how much cheaper does the servicing look now out of the dealer network ?