I had a pair of Marshmallows, JVC HA-FX34s and liked them because in their price range they did the best job of isolating me from the noise of the busses and subway cars I ride to work. The sound was edgy and brittle, and bass was light, but I was using them to listen to news and lack of sound quality was not a huge problem.
Recommend this product?
When my first pair of Marshmallows got lost, I went to the store, and bought a new pair; but these looked different, they're a second generation of the Marshmallow product, the HA-FX35. The new model appears reasonably durable, has decent volume when attached to my smart phone, and they come in a rainbow of colors, including boring black and boring white.
Though the new and old models are similar, the new ones are a definite improvement! The sound of the HA-FX35 earbuds is smoother and less fatiguing than their predecessors.
Other than that, how good do they sound? I won't say the JVC HA-FX35s sound great or sound awful because what you're used to has so much to do with how you perceive sound quality. If your last pair of ear buds were a $7 house brand set from the drug store, these will sound great to you. If you're used to very high end headphones or earbuds, these will disappoint you. I will say I think $20 is a fair price for what you get.
For reference, my day to day, go to headset is a pair of Sennheiser PX100 conventional walkman headphones, which are a great value at $35. I generally use the Sennheisers for music, most of it classical. For comparison I'm running some opera through the JVCs right now, and I'm struck by how thin and bass-free they sound and they have a closed-down sound about them compared to the Sennheisers. The closed down feeling probably has something to do with them sitting so deep in my ear canal. I won't be throwing away my conventional headsets any time soon, nor will I hold a grudge against the JVCs. That aspect of the JVC's sound quality, I'll assume, is just a tradeoff of the form factor.
And is it fair to expect Carnegie Hall sound from $20 earbuds? Probably not. Many users listening to pop music may just go with them and not obsess over the sound.
What is unique and valuable about the JVCs is what I referenced earlier. The earpiece uses cushy sound isolating foam instead of the silicone ear cup used by most other brands. In noisy environments this is a very nice thing.