Are you talking about the Platinum Elite spas sold through Costco? If so, I believe they are made by Hydrospa. There are some other spa forums that discuss this model quite frequently--both the good and the ugly. Most of the Elite owners have stayed away from this forum for some reason.
It's probably not a bad spa for $4,000, but I wouldn't call it a premium line. It sure isn't a $9,000 spa selling for 4K. I personally would stick with a dealer backed spa just in case you have problems down the road.