Correct. The reason is that the salt cell will last much longer, giving you better value for you money.
I initially you'll use a bit depending on the size if your pool (how many gallons is it?). After that, it doesn't get "used up" or evaporate. It will only get diluted if you replace water (i.e. after backwashing the filter, pumping out excess water from rain, etc). So if you don't have to replace a lot of water you won't have to use much boric acid to maintain the desired level.
The last time I bought a 55# bag was in April 2014, and I still have some left (maintenance only).