Yep good, I've used this approach before in a pinch but never tried to get really serious using it as a standalone/complete sharpening tool. But you are right: it is minimal.
Can you walk me through what approaches you use, what sharpening motions given the rounded and small sharpening surface? Do you use a push or pull sharpening motion? Do you go clear across so that each pass is hitting both sides of the ceramic circle on the bottom of the cup? Etc. Interested to hear how you do this. I like the idea of "improvised sharpening systems" that you can use when nothing else is available. I.e., I'm stuck at uncle Jed's house for thanksgiving, need to sharpen my folder, and forgot to bring my $900 Wicked Edge Pro system.