The only 'meso magnet' in Maple Story is the pet meso magnet, in which the pet simply picks up your mesos for you after you kill it. It is available in the Cash Shop and can only be equiped to a pet.

If you're talking about a meso magnet that literally absorbs all the mesos toward you, that is hacking and is a banable offense in Maple Story.
Does maple story mesos magnet helps you in battle?
All they can do is spiff up your outfit, you can name them, or put the following on them.

Meso magnet: If the pet moves over the mesos on the ground came from the monster that YOU killed, it'll pick that up.

Item pouch: picks up all items ton the ground came from the monster that YOU killed, if you move over that

The weird scale thing: lets you pick up all items or mesos on the floor, doesn't have to be from you, but you have to have meso magnet or item pouch or both.

Wing boots or something: lets your pet move faster