Anyone using the USB Port replicator with Video?

[umern]

Hi,
I want a dual digital screen setup for use with my X121e and have seen the following:
http://support.lenovo.com/en_US/product ... D=PD014492

But I am concerned about how much this affects the overall performance of the laptop. I am assuming that the driver that come with the replicator is going to have to pump all the video data etc over USB to the replicator and this will impact the performance. Or have I misunderstood how these things work?

Any advise of personal experience of using above device greatly appreciated.

Thanks!
PS I would expect to use the above with a 22" and 19" screen so pretty high resolutions on both. I don't generally use the laptop to watch video etc - mostly for normal office stuff and the occasional Adobe Lightroom and Photoshop elements stuff.