You won't have to replace them often. However, I advise having one or two on hand, like ink, because if it reaches zero it won't print anymore. You can find replacement foam sponges online that are a lot cheaper than a new cartridge. It's more messy, but a lot cheaper. That's the one part I'm comfortable using a third party manufacturer.
Although I'm a little surprised that it's at 53%, the initial ink charge is going to use a decent amount, so I'm not shocked. Can't remember what my 9900 started at.
If the 3880 has a drainage system from the borderless printing sponges to the maintenance cartridges like the 9900, using borderless will spead up how quickly they fill, but I can't say how big of a difference that makes.
Not sure if the 3880 works like this, but my 9900 has two cartridges, and I've never seen a cartridge installed on the left change its value by even a percent. (Probably because I never print borderless.) I let my original right cartridge go down to about 10%, then swapped them. I leave the 10% on the left, and just deal with the one on the right.