Anyone used the Lilliput 669GL (or any other inexpensive monitors) with a Mark III? I've heard good things about this with a Mark II, just wondering if there are any problems with the 3.

no any problems, and no blackout after you push REC,
I have a few different monitors from Marshall to no name made in China and they all work with 5DIII

I have a re-branded Marshall (LCD7-HDMI) but of likely Lilliput origin. Works fine with the 5D3 with just a few lags between screen. I can focus fast glass with it no problem, but the thing doesn't have good contrast or match exposure of the camera very well, so I tend to underexpose everything I shoot with it. I use the Zacuto Z-finder Pro with it most of the time, and I'm golden.

I bought the Lilliput 5D-II/O/P 7" 16:9 TFT LCD HDMI from Amazon a few weeks ago for my 5D2 and it also works well with the 5D3.

If anyone uses this combination, you need to hit the "info" button on the back of the 5DM3 a few times to get a bigger image on the monitor. It doesn't quite fill the screen, but it nearly does. And there's no delay or blinking going from stanby live view mode to recording (as Buba pointed out).