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Warranties don't usually transfer to a second owner so i would look into that some more.
These are both lower-line spas but should be more than enough for you. However, you need to realize that as a spa gets older, the maintenance that it received over it's lifetime becomes more and more critical. So, if the used one was well maintained, you may want to consider it but if it was me, I would buy the nicer, newer spa as there has been less time for someone to have ignored it.
Did you get the sub panel with the 30 and 20 amp gfci breakers?
Just curious, did you get the warranty statement in writing? Watkins does not transfer warranties. If the dealer is telling you that you will have a warranty for seven months, it's on them. Better make sure you get it in writing.
Update -- I was able to get the price of the Tiger River Caspian down considerably -- $3000 including delivery and install, all chemicals, 7 months left on warranty... so I did the deed. Should be delivered early next week, I can't wait! Thanks to all for your advice.
The warranty as it turns out is a bit of a tricky issue. The person selling it sold me that the warranty transfers, as they were told that by the dealer, but upon further inspection as you all pointed out the warranty is not transferable. Given that the dealer gave some... lets just say confusing counsel to the original owner, which caused them to tell me that the tub was under warranty -- they knocked a little more off the price AND since they were so confident in the condition of the price agreed to share in the cost of any repairs over the next 6 months remaining on the warranty. That seems more than fair. The cover ended up needing to be replaced which I guess is not a big surprise given that it is 4.5 years old so I'm trying to decide between a DuraTherm cover from Spa Depot or a cover from RH Tubs. Both look like good choices.As a side note, my original plan to put the tub on my deck turned out to not be such a "solid" (pun intended) plan -- so I had to have a a section out of my deck removed and then pour a pad. That happened last week, the tub was delivered and sat empty for a week until yesterday when the electrician hooked it up. I filled it with water last night (in 30 degree temps, so I was crossing my fingers that the heater would work.. it did). It was 49 degrees when I filled it, 83 degrees when I woke up, and if my calculations are correct should just be breaking the 100 degree mark. I guess this means its time for me to go have my first soak!