I have inline @ease on my Hot Spring SX, but functionally it should be the same as Bullfrogs. Generally speaking, I am happy with the system. Mineral cartridge lasts 4 months and I have gotten anywhere from 3-5 weeks out of my SmartChlor cartridge. I have noticed my pH and alkalinity drift downward with this system so I have to add alkalinity increaser every 10-14 days. Other than that, I am satisfied.
You likely will have actual Smartchlor cartridge life of 2-3 weeks on larger hot tubs. If you have to use the higher settings, you cartridge will empty quicker. If your pH or alkalinity bottom out, the cartridge will empty quickly. If you are looking for a proven system that is easy to use, I think this is a great option. If you are looking for the least expensive way to treat your water, I would go another route.