Product review (5 stars): Cheap enough to let you lower your maintenance and call out costs by changing filters regularly
Genuine replacement filters in a single four pack, which at the current price here on Amazon equates to less than $10 a filter.
That's a great saving.
I use a local heating and air company who have served me well for years, and never ripped me off, and they usually charge around $15 per filter when replacing.
Manufacturers recommend that you change the filter twice per season, so around 8 times a year or every 6-7 weeks.
I have gotten into the habit of setting a calendar note to do just that as my regular servicing is only done twice a year.
I don't think that the water is particularly "hard" where I live, but the filter does get very lime scaled up, and recently leaked out of the unit onto the floor as I had not changed it in a considerable time.
Having these inexpensive 4 packs means I can change the filter myself in a timely manner without having to call anyone out.
The effectiveness of the filter does make a difference, I have a humidity level sensor in my house (forced air central heating) and try to keep the inside levels at around 40% for comfort and to minimize static. Old and clogged filters will effect this visibly on the monitor over time, as well as having the humidifier on the correct winter/summer settings.

On a closing note, the filters out of the box new look like they are already full of limescale, they are not. That is the manufacturer treated metallic weave of the filter, just in case you are concerned.