My Marquis has a built-in bromine feeder, the frog in-line system, that uses the bromine cartridges. I learned early on that I could reuse the cartridge and find I refill it about every 3 or 4 weeks in the summer, a little more often during the Fall & winter. The cartridge holds about 10 each 1" bromine tabs. It's set at two unless I have heavier usage (Normally, my wife and I, sometimes my daughter and her friends).
I've had my Marquis since June 05 and I haven't noticed any difference yet in the weight of the cover.
As always, "Your mileage may vary". Even if I did have to replace the cover a year or two sooner, it would be worth it. Once I'm finished with my soak, I turn off the jets, close the cover and walk away. I don't have to throw in any chemicals and (hoping I don't forget) come back in 15 minutes to close the cover. If I'm out of town for a few days or a week, no problem. The tub will be fine.
pg_rider,
Keep an eye on it every few days and before you know it, you'll figure out the routine.
Phil