From looking at SD'd website and what J McD's said, I intend to agree. I was leading toward the 'get a $99 boombox from Target/WalMart', but then saw the builtin, retractable marine-grade speakers (which would be about at ear height, and would give you about normal stereo separation, if you are in the middle of the spa....). The remote is more gravy, and marine stereos do tend to last for a good while. I've had boat units last for many years, but no way to tell what exactly is used by SD, of course. (Mine were in salt water, but how does that compare to a spa with chlorine/bromine?)
The added benefit of the subwoofer in the shell is fun also!
Bottom line, only you can measure if the extra 'fun' of the built in toy is worth the added cost. I think I'll go for it for mine!!