Gerbils are highly territorial, and can be very aggressive. They can be good pets if they're handled from hopper-stage on, but they're very, very aggressive to each other throughout their lifetime, and both males and females will fight to the death if they feel threatened by the other (if the habitat is too small, food is scarce, if one female has babies and the other doesn't....). They're also very smart and excellent escape artists. They're more like rats in a lot of ways than mice.
As pets, I think they're a better choice than mice or hamsters if you're going to have just one and not co-hab them, because they do learn their person and can become quite tame and easily handled. As a feeder, though, I think they'd be hard to manage.
Gerbils were my first breeding attempt at age 10 or so, when any color but agouti was still rare enough to be easily sellable to local shops and sold at a premium, and I quickly learned that breeding wasn't nearly as easy as biology books made it sound!