I've had the HP4 for about 4 years now i think, and nothing has failed on mine yet. I also agree that it's clean, i don't really notice any coloration, but i mainly use it for tracking.
One thing i've noticed on mine is that the stereo image drifts a a little at lower settings, and it's not consistent between the 4 channels (I.e. output 2 on mine is the worst, drift is almost up to 1/3 of the way, but input 4 is basically perfect expect at extremely low volume). It's been like that since i bought it. Not really an issue during tracking, no one really seems to be bothered by it, but it might not be the best for mixing. Mine is the older model though, the newer ones may have better pots in it.