Product review (2 stars): Just not as good as the real ones.
This is my impression after running with the pads for about a month. They look the same but are just simply not as effective in getting water into the air as the real ones.  I have the aprilaire 400 series. The way these work is that there is a reservoir of water at the bottom. Water flows down through the pad from the top to the bottom periodically  to refill the reservoir.  The key to the whole system working is the ability of the pads to wick the water  up from the reservoir and into the pad where it can be evaporated into the air.  With the manufacturer pad I get at 20-30% humidity readings when the heat is running.  Since I switched to these to save some money I'm never higher than 16%