Nakky's really not as bad as Eripon. She has this cutesy idol voice that isn't associated with good singing (her solo version of Kimi Chari is godawful because of her voice), but Eripon tends to sound sloppy and doesn't hit the right notes in parts that aren't even too high or low.
[youtube]LwkIpn6Gyjc[/youtube]
Also, I just watched C-ute's recent winter concert DVD last week, and compared to Mai, I find Nakky to be soooo much more enjoyable to watch because Nakky's expressions are always excellent, whereas Mai doesn't smile 80% of the time, and that actually makes her performances come off as seemingly half-assed sometimes (like her solo of Momoiro Sparkling, which is a happy song). And normal Nakky >>>>>>> cutesy voice Maimi (which comes out more often than we want and makes me want to throw something at the screen sometimes), so I found Nakky's performance quality to be 3rd in the group behind Airi and Chisato, and those two (especially Airi) are pretty damn impressive.