scale inhibitor?

I need to order a new liff scale inhibitor.
what is the difference between a limefighter which is magnetic,
and a limebeater which is electrolylic apart from the price.
Is one better than the other?
I have a limebeater that is nine years old and needs replacing.
I have spoken to a plumber who was no help who said he has
never had to replace one.
I am so confussed can you help?

thanks linda