Overall, the the Gumy Plus is very pleasant-sounding for the money. The bass isn't huge, but it's relatively tight. The treble isn't quite as smooth -- there's a touch of harshness -- but it isn't offensive. The sound compares favorably to many earphones in the $25-$35 range, though the JVCs didn't offer as detailed sound as the $49.99
I also compared them to iLuv's City Lights. Those earphones serve up a lot of bass for $7, which is probably why a lot of people like them ("contemporary" listeners seem to love bass these days). Both the JVC and the Panasonic have better balanced, slightly clearer sound, with the HJE120 delivering the most natural and accurate sound of the dirt-cheap trio.
Conclusion I'm not sure if all these sub-$10 earphones come out of the same factory in China (they probably do), but there are now several models that deliver an excellent amount of bang for the buck. I had a minor quibble about these earphones' top-end (treble) performance, but in all they sound very good for the money -- and they're lightweight and comfortable.
If you're looking at these versus the competition, I'd say the Panasonic ErgoFit RP-HJE120 sounds a touch better, but the one drawback of that model is that the cord has a tendency to get tangled. And if you're a bass lover, you'll probably be more satisfied with iLuv's City Lights earphones.
Of course, you could buy all three models and do your own comparisons. The three combined will only set you back a little more than $20, and if you add a fourth (and get past $25 total), you'll qualify for free shipping on Amazon.