It all comes down to your expectations. The parks are generally ok to decent with the rare exception that there is a really nice park. But generally speaking, the price is hard to beat if you buy an aftermarket membership.
There are quirks-
1) All of the sites are first-come, first-served. You reserve that the park will have a space for you but it might not have sewer or 50amp service. You don't reserve a specific site or level of site (with the exception of handicap sites).
2) Only some memberships allow you to leave one TT park and go directly to another once you stay 4 or more nights at the first one. Being able to is generally called "going park to park"; not being able to is called "2 weeks in/1 week out".
3) The parks are pretty sparsely located. There are about 80 parks around the US that your membership will allow you to us. Are these in areas that you want to go?
4) Some parks charge extra for 50amp spots if you're on one. Even if you only have a 30amp rig. If you're on the spot, you get charged for it.
For us, we are full hookup RV parks kind of people. We've spent/planned for 180 nights in our camper and of those, 65 are TT park nights. My membership dues are ridiculously low (mine was an old 1970s hand-me-down membership) and it works out to $7/night for those TT park nights. Including that and the cost of actual nights in other parks- my overall average nightly rate is at $29/night. Which means, TT saved me about $1,500 per year in camping fees.
Like anything else- it's a good deal if you make use of it.
