If you haven’t been searching for something like this, trust us, it hasn’t been looking for you.

For years, nearly every Mac has been able to connect to a second display. Laptops and iMacs include video-out ports, and Mac Pros ship with video cards that connect to two displays by default. The low-end Mac Mini is the only one with a single video plug. With that in mind, the Gefen USB to DVI adapter fills a narrow niche, turning a USB port into a video connector for an extra display. The process works, but it’s so burdened by problems, that we can only recommend it to the truly desperate.

The high-speed USB adapter connects to displays through a DVI plug, and it also includes a VGA adapter for older hardware. Just install the software, and plug everything in. In our tests, this was the best aspect of the product. System Preferences added the second display without any problem, and we could even set it to rotate the screen in 90-degree increments for vertical installations and other special situations. Since USB is hot-swappable, we connected and disconnected the extra display without having to turn the Mac off.

The adapter supports resolutions up to 1,600 by 1,200 pixels, but we can’t imagine using it regularly because of its abysmal refresh rate. At resolutions higher than 800 by 600 pixels, you only get a 60-hertz refresh rate. This means that a CRT will noticeably flicker during use, causing us strain and even mild queasiness. (LCDs are still legible at this rate.) And don’t bother using it for much more than text apps; the adapter doesn’t support OpenGL acceleration. OpenGL is a core component of OS X, and without acceleration, high-res movies stutter, iMovie won’t launch, iPhoto slide shows don’t work, and the interface is generally choppy, among other problems. Gefen says it’s relying on Apple to add support for OpenGL acceleration, so it couldn’t say when—or with certainty—that’ll happen.