I've had this for a few years.   (You need to Login or Register
It's not perfect but it seems to do the job well enough when you're like me and don't give yourself the patience needed to do a good job with a flat stone. It's small, light, cheap and does alright with a fillet knife. Doesn't seem to work on thicker knives like what I use for butchering deer, but that's generally not an issue tripping.  :)