Better Solution: Duet Display
 

For all Mac users who are looking for a good alternative you should check out http://www.duetdisplay.com for the iPad. The iPad can be used as USB-connected external display, similar to displaylink displays.
This app has been developed by ex apple employees and shows that USB-displays can be fully functional without any bugs.

While Duet Display seems to be more responsive all-round when compared to DisplayLink monitors (on Yosemite 10.10.1), it's far from "fully functional without any bugs".

It also seems that you can't use a displaylink monitor and duet display at the same time without it causing some fairly major issues (like the DisplayLink monitor failing to refresh properly) or the Duet Display screen to lockup. Removing the DisplayLink driver stops the lockups/refresh issues, but then obviously you can't use that screen.

These are things I've just noticed after around an hour of use too.

On the upside, the Duet Display monitor plays full HD content as fluidly as it does natively on my iPad Mini Retina, and the screen touch support is pretty cool too.
I'm going to wait until the developer has released a few updates before I decide if it's a better solution in general or not.

DuetDisplay does mostly work well, but even with an iPad 3 on a new Mac Pro, it lags a bit at 60fps. 30fps is nice and smooth. Doesn't automatically launch at login.