how good is access to other affiliate campgrounds with CC?

We used C2C for the 7 yrs we FTd.

Making reservations for the various CGs was easy....all on line via C2C website.
that includes the Good Neighbor, Encore, Thousand Trails parks

As with any affiliate membership SOME restrictions did apply.
Direct members of the parks have Priority so some dates were blocked out for those members use.

Over all.......it WORKED.
Didn't use it ALL the time, we use COE, State/National, City Parks, Fairgrounds,
BLM/Boondocking, even used Passport America at times.
Being FT we were flexible