Product review (4 stars): The botttle valve caps are worth the cost, and look likely to work longer than the OEM caps, which worked for 8 years.
I got 8 years out of my original bottle valves, and the 11 gal/day Emerson works great for our 4 room apartment. $21 is ok for a $130 humidifier. I finally got a good whole house unit for a bigger home we had in Delaware, that was installed on the gas furnace, and digitally controlled the humidifier dead on the setpoint to 1 %, checked with a lab meter. Don't ever set it over 50%, since it grows rug mites quickly and makes the air worse than dry. But the whole house unit was $500 installed, and even more trouble for filters and autofill adjustments.  So I am back to the Emerson and it works great for us on low, using 6 gallons a day.  If I did not block the apartment fresh air vent most of the time, it would use 15 gallons a day, making filling much more trouble. I don't think my neighbor below me in our apartment wants me to get the auto-fill attachment for the unit, which is also a long way from any water pipes. I used to be able to carry the three gallon bottles easily, but now, at almost 80, I get help.  If someone has the math model to make the valves on a rental 3D printer, you could make 12 at a crack for only $85 and save $65, if you ever needed 12...