No, I've not bought one yet. I am the "proud" owner of a Little Giant 3-MD-SC... though it's a tad noisy for my taste, and it runs very hot. However, I'm hoping to buy the WMD-20RZT once my student loan documents come through (since I've already paid for school... got to love that government aid eh?)... all I have to do is "convince" myself that it's needed.
One thing though... I'm not sure that the Iwaki pumps were originally intended for aquarium use, though I agree that they seem perfectly matched to the job. The company in my area that sells them sells equipment for moving chemicals and stuff like that.