I’m trying to get three monitors with my laptop setup (my laptop screen + 2 additional external). I have 1 external already extended to via HDMI port in my laptop but my main question is will any of the external usb 3.0 graphics cards allow me to extend to a third screen? I have heard many reviews that say that these cards will only extend to 2 screens then the rest must be duplicates of another.
Hi Ryan,
Thanks for posting your question here! Here is a video that shows six external monitors connected through our USB 3.0 adapters connected to a Windows 7 laptop via our Plugable 7 Port USB 3.0 Hub, all in extend mode.
As you can see if we can have six external monitors in Extend mode, you can definitely have three. 
Hope the above information helps! If you need any additional information, please do feel free to shoot us an email at support @plugable.com. We are here to help!
Regards,
Roze