@stuartv : You don't find the magenta lenses too dark at lower recreational depths? Do you know the difference between the Sea Vision 2000, 2100, and Ultra (2200?) But I do like the idea of those HydroTacs.
I have done a few dives in the 100 - 115 range with it where the viz was only 10 - 15 feet (so, deep-ish and turbid water combined) and didn't have any complaints. But then, I didn't take a clear mask down and compare them, either. Deep where the viz is decent, the magenta is great.
That said, if I know I'm getting in where the light/viz will be poor at the bottom, I would more likely use the yellow lens mask. The magenta is really more for blue water, which kind of implies at least that the water is pretty clear, offering good visibility. If it's really clear, but you're going deep and the sky is overcast or something, then I think the magenta lens would give no real benefit, but I don't feel like it would make it dark enough to be any kind of issue. I would not hesitate to do a night dive with the magenta lens, if it was the only mask I had with me (thought it obviously wouldn't be my first choice, if I had either of my other masks).
If you already have a clear mask that works well, except for needing reader lenses, then why not get a magenta with readers and put Hydro-tacs in your clear mask? If your clear mask has other issues for you, and you only want to buy one mask, then maybe it would be better to get a clear lens, so you know it will work any time, any place.