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HotSpring Spas, the World's #1 Selling Brand of Portable Spas and the Industry Leader for Over 20 Years.Terminator
This is straight from sundancespas.com."Since opening its first manufacturing facility in Costa Mesa, California in 1979, Sundance SpasŪ has grown to become the world's largest manufacturer of acrylic spas. An international manufacturer and distributor of the most technologically advanced, well designed, and durable spas in the world, Sundance Spas can be found in more than 700 retail locations in over 51 countries."I guess this means Sundance has the most spa manufacturing plants and Hot Springs sells the most spas. :-?
Since there is no independent auditing, we will never know. Each claims to be the biggest.