[wildly OT] USB->VGA's ever any good?

[Nick Sabalausky via Digitalmars-d]

Apologies for going so far OT, but couldn't think of a better place to ask.

Anyone know if those USB->VGA devices out there are any good? Also, 
reasonable Linux support with them?

I imagine HDMI->VGA is likely junk, since they'd presumably be limited 
to 60Hz output, which is just masochistic on a true VGA monitor (ie CRT).

But I dunno about the USB stuff. They would essentially be their own 
independent video card, right? Bypassing the PC's internal GPU. Or do 
their drivers take the framebuffer from the GPU and send it out through 
USB? In which case, would there tend to be some display lag?

Heck, I wouldn't even be asking, but it seems that getting native 
VGA-out on a laptop these days limits your options somewhat.