I've done it a few times. It's a decent ride, pretty flat as 100s go, it's well signposted and there will be loads of others.
A few points to note though.
The organisers push it as a charity ride - however no part of your fee goes to charity. If you want to collect for charity thats on top.
Unlike most proper "sportives" the feedstops are not free (or particularly well stocked).
A large number of riders will never have ridden in a group before, some of the riding is best described as "unpredicatable". This is especially noticeable after the 60 mile route rejoins the 100. It's best to set off very early to avoid the majority of the "numpties".
Despite the above it's a decent day out, and a fun experience.