By replicating similar circumstances to the GF things are likely to be okay, they've had a lot of testing. But if you do try another cleaner make sure its one that doesn't gas/foam excessively. By way of example, I tried an oxy cleaner some months ago that was ridiculous: a tiny bit in a cup of hot water lost more than half of the volume as foam climbing out. By contrast others have been much calmer, whilst PBW just fizzed a bit on the surface - and cleaned more effectively too.
The magnetic coupling is just the way the driving (turning) force is transmitted to the impeller, the impeller isn't entirely suspended by the magnetism in these pumps. Instead it has its own little shaft to do that, and subsequently there are (plain) bearing surfaces. These are lubricated by the liquid, which also helps keep the impeller centred, which is why the pumps should not be run dry.