Do not use it if you have quality knives. What it does is improve the blade's performance, but it doesn't last long. Essentially, it destroys the cutting edge geometry by removing material in the wrong direction. Perhaps for some cheap knives, it makes sense to only use the ceramic edge for "light" sharpening, with very light pressure to minimize damage. All tools of this kind seem user-friendly and are relatively (to very) cheap, but the result is poor.