@DianeRuth I use an 18.25"" laptop with a 22"" second screen - both are set to 1920x1080. There is an adjustment in the riser that controls tension and thus the effort to raise and lower. I have set it so that I can lower it with one finger and raise it with two. It can be adjusted easier, but then when I'm lazy and rest my hands on the keyboard it wants to creep down. I'm very satisfied with its adjustability.
Not only is it good for mixing standing with sitting, I like it a lot when I come into the office for just a minute or two and sitting down seems like such a commitment. :-) I'm definitely going to call the manufacturer and see if there is a way to fabricate for an additional 2 screens. There is enough hardware (holes for screws) on the riser to receive another bracket that could hold 2 more screens!!! (email, Web, Remote Desktop and a spare for PDF's and whatever)