Wow, this is great
So I just got this not too long ago and have only used it once, but that's all I've needed so far (it's been 3 months since I got it).  I developed the dry type of callous.  The one where your skin cracks and the bottom of your feet gets white and a bit stiff.  This resolved the problem in no time.  IT'S STRONG, so watch out, but it gets the job done.  I don't know how it'll work on different types of callous since I know some people have the callous type that looks like the bottom of your feet is leather-like, so I can only speak for the dry, cracked type.  Great purchase.  Also, I don't know how to get replacements, so I'll repost once that time comes.
Rating: 5 stars