Got my M215W today and I'm pleased to say that Real D glasses work better than the zalman glasses. It's just a shame that I shelled out £10 for a second pair with the monitor.

Just adding: They should work on old zalmans as well. In this case i think (not totally sure) that the original glasses are a tad batter.

The RealD glasses do work, but they are not the exact polarization as the Zalman brand glasses. At least with the 22" model (ZM-M220W) I get this weird purple haze around ghosting images. Its not horrible, and a lot of the times I will use the RealD glasses to just watch a quick video on YouTube3D. However when I am going in for a gaming session or watching a 3D movie I will always use the real Zalman-brand glasses. They are certainly a step above. Maybe the polarization was altered slightly for the newer models, but I doubt it seeing as I have the new glasses and they work perfecly fine on the old monitor.