We just bought a single zone pass to test them out. We'll be in the western part of the US for the next year, and figured it would be a good way to save some money. It's already paid for itself in the first month and a half. We have reservations for another two week stay in August, and will use them as much as we can.
I think the key with Thousand Trails is managing your expectations. If you expect all luxury parks, with immaculate grounds, you will probably be disappointed. If you are ok with older parks, often with 30 amp power, and some sites without sewer hook-ups, you'll be fine. My wife and I have always stayed at budget accommodations when traveling be it campgrounds or hotels, and so far have been satisfied with our stays. The park we just left was one of the older ones, but it was clean and in good repair. We've been to another where many of the sites wouldn't fit a big rig, or were pretty far off level, but still found a site that worked.
Tom M. 1998 Safari Serengeti 3706,
300HP Cat 3126 Allison 3060, 600 watts of Solar.
Fisher and Paykel Residential refrigerator