Limescale forms when dissolved minerals—especially calcium compounds—come out of solution and deposit on surfaces. Because RO reduces many dissolved ions, an RO system can substantially reduce the mineral content of treated water.
But there is an important distinction
RO treatment at a drinking-water point is not the same as softening all the water entering your home. An under-sink or countertop drinking-water system will not necessarily stop limescale throughout the shower, washing machine or central heating system.
If your whole house has a limescale problem
Investigate whole-house water-softening options separately. If your objective is simply better drinking water and less scale in a kettle used for filtered water, a drinking-water treatment system may be more relevant.