FWIW, I have an Iwaki MD30RZ. I used it on my brew system for years, but only pumped boiling wort with it for the past year. Previously I was pumping water or wort at 180°F or less. I noticed some some hairline cracks on the back of the impeller, so I bought a new pump (Chugger).
My pump had "barb" connections not threaded connections. A friend gave me the pump; it had been used as a coolant circulating pump I think. It ran smooth and quiet. The magnet on the impeller is huge compared to the impeller/magnet of the Chugger.
Overall, I was very happy with it. I think that by running boiling wort through it when it's not rated for that probably caused the cracks. It still works, but I am concerned about the wort being exposed to the bare magnet.