They sound bad, when using the pitch control they introduce harmonic distortion to the sound and a ringing similar to that of the aliasing you get on a vintage sampler.
You can especially hear it on kick drums. This is even with the pitch lock off and latest firmware.
Don't have a good ear and can't hear it? Make a CD with some sine waves and check the output with something like http://www.audiotester.de/
The DZ's really are a load of dog poo. My friend has quite sensitive hearing and he totally hated them which is a shame cos they are nice to use but just sound shitty.
Pioneer's don't do it or even the original Technics SL-P1200. Pioneer gets a bad rep and I hate their mixers but their CDJ's especially their later ones I don't think are that bad