I would suggest shopping around. There are lots of independent warranty providers and you may get a cheaper deal or better level of cover with someone else (you can always challenge your local Renault dealer to match the price).

The key bit about an extended warranty, however, is what's listed in the policy exclusions. For example, a warranty product that excludes 'wear and tear' will effectively exclude 90% of the things that will go wrong on a 3+ year old van.