"Nonny" wrote

While a full variable speed controller would be nice, I wonder if it
really adds that much to the benefit of the fan. For instance, the
louvers of the fans require a minimum amount of pressure differential for
the air to open them, eliminating the lowest speeds you could get with the
controller.

I always start my fan on high for a couple of minutes to get the air
flowing. Then I can turn it to the lowest setting and it works just fine.
I like the variable speed and set it according to the needs at the moment.