From reviews, people find having a built-in speaker useless or ingenious. It also comes with earbuds, and Samsung now even makes a similar model without the speaker.
If you have private space and don't like to fuss with earphones, you might enjoy having it. The sound quality is pretty good. People reviewing it all seem to comment that the sound is surprisingly rich and full and not tinny as you'd expect from the tiny speakers.
I listen to podcasts (for fun). As a documentation guy who's a contractor, I record info-gathering meetings with engineers and project leaders and developers (with an Olympus digital voice recorder, the Samsung YP-K5 is just for playback), then listen back. It improves my retention of info significantly.
It accepts WMA files as well as MP3. It also displays JPGs, but I've never tried that feature.
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