I retired one when I started using good knives. It's not that they directly damage knives, but the magnetic attraction was not always sufficient to hold a heavy knife, particularly if the knife was not totally dry.
I have used ceramic knives for the past few years. They are the best - a bit expensive, but will stay razor sharp for years - possibly for life if cared for.
They are, however, not magnetic, and even if they were, it would not be advisable to put hem on a rack, since they can break if dropped.
I bought a magnetic knife holder in Ikea (it was a fiver a few years ago) it's really strong and I have very heavy professional chopping knives on it! Highly recommend it.