Blimey, it works! 2x USB monitors with 2.3beta on 10.9.5
 

Well, I just installed the 2.3 beta on my 10.9.5 system, and to my surprise when I rebooted, the second monitor burst into life. That's a first!

For reference, I have a Toshiba Dynadock connected to a new MacBook Air, with one monitor on the DVI socket, and the other on the HDMI. I also have a monitor connected to the thunderbolt, and the laptop's screen too. So that's four screens!

So when Displaylink works, it's wonderful. Problem is I haven't risked unplugging my laptop yet. I will tonight when I go home. I wonder if it will work again in the morning. I'll keep you all posted!

That's great news - how is the setup working now that you've used it for a couple weeks?

It's not 100%, of course. It doesn't remember my screen layout, so every time I plug in the laptop, I'll need to set up the arrangement, and move the windows around - but that's only a small inconvenience really. Slightly more annoying is that sometimes windows and dialogs get 'stranded' on screens that no longer exist, after I disconnect the dock.

The big issue for me is that I feel I'm now stuck with this delicate solution - that if I upgrade to Yosemite, it will break again, and I don't know how long I'll be willing to stay on an increasingly old version of the operating system.