I have one of the early versions of ACE, so I don't know if it has changed over the years, but mine let's me adjust both for spa size and usage. It also has the temporary boost option. I agree 100% on ease of use and maintenance. After water changes, I make sure I nail my levels up front and get an appropriate level of CYA (typically 25-30ppm) and borates (35-40ppm). From there on out it is almost completely predictable with very little drift until the next fill! When I first got the tub, I tested religiously on a daily basis with a Taylor K2006... Now, in the summer months, I've been testing biweekly and it's very rare that I have to make adjustments, even for pH. In the winter months, I use the tub pretty much daily and still do need to add muriatic acid to account for pH rise with the jets and water features over extended time (2 weeks or longer). That said, I've gotten to the point where I'm only checking once a week in the winter, unless I get an off reading or have more or heavier usage than normal.