In defence of the RAB…
They do everything for you.
Route signage, feed stations, breakfast & dinner (as much as you can eat, full cooked breakfast, the works), mechanical support, luggage transfer, tent pitching and de-pitching, they supply laundry service, showers, toilets, charging points for phone/GPS.
You don’t need to spend anything for the 9 days that you’re doing it.
All you need to do is ride your bike. It’s like doing 9 Sportives in 9 days.
Downsides:
you’re working to someone else’s schedule – you HAVE to reach the end point, there’s no bailing half way and sorting a B&B if the weather is shit one day, likewise if you’re feeling good/have a tailwind, you can’t just keep going.
sleeping in tents isn’t for everyone but they’re decent enough.
riding with 700 others of wildly varying ability (although once out on the road, you tend to form your own little groups and it’s pretty quiet).
No choice over the route – you follow the arrows, you can’t wander off into a little village or decide to take that road instead.
Depends though – it’s always oversubscribed, there are plenty of cash-rich, time-poor people who don’t have the time/inclination/confidence to do their own planning and navigation and logistics or who want to do it but can’t find any mates who are interested. They don’t want to do it alone so this is a way of getting some company.