What happens is this story is told at the time of the sale and the pitch sounds great. What you're not being told is that you may have to upgrade your pump(s) so the addition of these extra jets doesn't decrease jet performance.
Excellent point. When I first started evaluating Arctic Spas, the dealer gave me the same sales pitch about upgradability if I didn't want the Legend Extreme package (includes all available jet options). My first observation in response to that was the fact that the Legend Extreme package also comes with an extra pump to power the added jets. The dealer acknowledged that two pumps might not be ideal but I could always shut off some of the individual jets manually to compensate.
Considering the upgrade cost was quoted at $250/jet, that suggestion really seemed to defeat the purpose