I am new to the overseas game, only 2 seasons worth but I have found them to be excellent. They only work out of season. Most sites are very good (so far).
They last for 2 years. You get a book and the cheques. My only problem is the directions to the site. They can be rather vague, unlike Caravan Club directions. I have found it is not a bad idea to cross reference them with Caravan Europe directions.
The only additional cost maybe tourist tax, which is about a euro a night.
Alex