I'm no expert on dehumidfiers, but we do have one in our basement where we have a dampness problem. Yes, it does help. I also had one in the basement of my first home. The one we currently have drains into our sump pit. That's handy. I had to empty the drain pan in my old one by hand and that can get old. The one we have now also has a meter that measures humidity. That's handy, too, so that it doesn't over dehumidify (which not only makes your air too dry, but also costs money). That's generally not a problem in our basement, but it ran far less this past summer during the drought. Noise is also an issue from the free standing units. I'm not sure if they list their decible level, but I know that I wouldn't necessarily want to listen to the dehumidfier in our basement all the time. But you could have yours set to run when you're not home or, if you get one with variable fans speeds, run it on a lower speed when you're home. A whole house furnane could be an option, too, although likely more expensive. I will admit that I don't know what our humidfier costs in terms of electricity.

If memory serves, they're often rated for how much square feet/square meters they'll cover, but I think that's just one factor to consider when deciding what size to get. The other is just how humid the room(s) are to begin with. Have you ever measured the humidity of your apartment? Also, do you have an exhaust fan in your bathroom? If it's not doing a good job of clearing out the humidity, you might consider upgrading it. How long do you typically run it after a shower? I've seen suggestions that they should be run longer after a shower than they often are. We run ours for about a half hour after every shower because it's not a particularly powerful fan.