PCM2. I hear what you are saying about the new Dell, but I would steer clear of brand new models. At least wait till some reviews are out and any problems in production, are ironed out.
With the ZR24W, he is getting a tried and tested product which rates high amongst most users. If he gets a brand spanking new DELL, he will not only have to wait for it be released, but if he adopts early, he will most definitely pay a higher price and also, he may get a product which isn't as good as the ZR24W.
If he is in no rush to buy, then there is no harm in waiting to see how the DELL pans out and if the reviews are good...then he can buy.
Most of Dell's recent monitor launches (the narrow gamut ones) have undergone fairly superficial changes since their introduction. Their older models, most noteably their WCG-CCFL models, were plagued with issues and were revised several times on the hardware level. There is no reason to think that the U2412M won't be a fantastic monitor straight from the off - but obviously the reviews and user experiences are worth paying attention to first. It doesn't sound as if monographix is in a massive rush as he is looking to upgrade what one would assume to be a fully functional monitor.