Product review (5 stars): my local ace hardware was selling them for 69. ...
my local ace hardware was selling them for 69.99 while amazon as offering them 20 dollars cheaper!

Worked as expected. I have an old Aprilaire 550 and although this was not the exact same, fitment was the same. It mounted to my humidifier as expected and fit the waterlines the same.

After reading all the reviews, it seems people aren't checking if this solenoid is compatible with their humidifier unit.