If they do the job, magnets or not, why worry about it?
Interesting note - I put one on a Jeepster I had (a Hayden?) - in front of the radiator. I used a simple on-off switch. I also had a green light by the switch to remind me it was on that illuminated with the fan. Nothing complicated - KISS.
When driving down the highway I noticed the light came on - with the fan switch off! Thought something was awry at first.
The fan was turning from the air blowing through it, and the fan motor was acting like a generator, powering the light.
So the fan motor must have had permanent magnets.
It even did it when not driving, just facing into a breeze. I had fun with it, I told a friend that's how I kept the battery charged - he believed it!