Product review (4 stars): Solid filter
I have two humidifiers, a Vics and Sunbeam (both models listed as compatible) that take this filter.  The Vics is shaped in an oval and the Sunbeam a circle, since the filters are malleable you shape it to fit.  I believe I read one review that said the Sunbeam smashes the filter down, mine does as well but it's very minor and doesn't affect function.

I run the humidifiers every day (with water in the winter and without in the summer) as both a white noise for the kids while sleeping and to add moisture to the air when it's dry out.  The filters last roughly two years.  I'm not sure if running it dry has anything to do with that or not but I feel I get my dollars worth out of them.  While I haven't tested many different filters I feel these do a good job and haven't had any complaints.