If they want peace and quiet then Westward Ho! is not for them!
I would get them to think very carefully about where they go. My parents lived in that area for many years - but rurally (2 miles from a village). It was fine when they were working/newly retired (in their 60s) as they could go where they wanted, had access to what they needed. But they wisely moved away in their late 60s to be in a town in Herefordshire where they could walk to shops, where there is a bus service, and where they can access healthcare.
In Devon, there aren't many hospitals, so if you need access to any kind of specialist treatment you could be in for a lot of travelling (on busy/small roads). Many villages won't have GPs (or any other services) so you have to travel for everything.
I think there's quite a difference in living somewhere for a long time, where you may have family/a wide social network/community who you can call on, or do mutual favours for. If you don't have support, it may not take much for life to become quite challenging.
Maybe they're taking early retirement in their 50s, and this is a stepping stone to something else, but if they're looking at a long term retirement plan, I'd be thinking hard about what kind of access they might want to shops/services/healthcare in the future, and plan accordingly.