There are many reasons for and for not full foam.
I've yet to see any real evidence of truly 'better' energy efficiency in the long term, and yes, full foam can be a technician's nightmare if freeze-ups or other types of accidents or plumbing malfunctions occur... but they're quite rare.
Most of the leading brands use full foam. In the 8 years I've been in this business (as well as hundreds of spas repaired of almost every brand), I've only seen ONE major brand (which will remain nameless) have a problem with this due to massive blower injector failures. This was the jet mfgr problem, not the spa mfgr. Otherwise, you should probably never have a problem plumbing wise with a full foam tub.
So, take that as an endorsement itself. But on the "dark" tech side, you'll always here that we prefer to be able to 'get at the guts' when we want to, not when we have to!
All that said, like I've said a million times before, ignore the horsepower and tech specs. Pay more attention to the seating positions, comfort, number of jets, whether or not you can get a dealer to throw in full professional electrical installation on the cheap, an ozone generator, and always.. always try to get an upgraded cover (not a cheapie - as some of them are - [not all though]) with your new spa. All of these things are usually negotiable!
And Marquis makes a really nice spa. I wouldn't worry too much about longevity with this kind of issue. Unless of course you're likely to leave it full of water and turn the power off in the winter. In which case I wouldn't buy a spa at all!
