The unit I received has a VGA (DB15HD) input jack, which did limit my testing a little bit. I’d have liked to try a few old consoles like the SNES, for some classic SMW comparison shots, but I have no way currently to get a SCART signal into the GreenAntz. Instead, I decided to go for most of my testing with Supermodel, that being the flavour of the month with gm-matthew’s recent full-speed network builds. Testing was done at 480i, though I'm aware others are getting similar results with 240p. The GreenAntz is powered by a USB C plug, which was super convenient for use with a PC.
I can only say I’m impressed. I was testing the output of a crt_emudriver-enabled laptop on an Ikegami TM10-17RA 10” 450TVL shadow-mask 15kHz broadcast monitor, and with the contrast and chroma set right I would genuinely struggle to tell the difference between RGB and YPbPr. To the point that if someone else had set everything up I’m not sure I would have been able to pick which was which. The little Ikegami is a fantastically sharp and vibrant unit, and there was no loss of colour or sharpness at all. There was perhaps the tiniest of colour balance differences – which is more than made up for by the fact you can dial the chroma up for extra saturation if you want to. That’s the main reason I like having a converter even though all of my setups take RGB.
I was a little confused by the colour balance pot on the unit, as it didn't seem to do much. On speaking to Zeb though, he explained how colour-accurate the circuit is, and that the difference the pot makes it hard to spot with the naked eye, and more something to be measured with a scope or sensor. He also mentioned that the pot might be left off future models as it's not really needed. I'm also aware of how much work he's been putting into the sync conversion, so i imagine if you're having trouble with sync then the GreenAntz might be work a look.
There's now a switch to have the unit take C-sync or separate H- and V-sync, which makes this an option for MiSTer as well (say, if you want to skip the IO board and get better video from an HDMI-to-VGA dongle. You'd get the GreenAntz for about the same money as the IO board, though you'd need to think about a VGA to SCART cable, mb, to use it for consoles as well. Still a cheaper option overall.)
I know how much work Zebidee has been putting into the GreenAntz, and it really shows. There are a number of great RGB-to-YPbPr converters out there, and this is certainly one of them.
If you want to buy one Zebidee is taking orders, i think. He's a member on here, and is also on AussieArcade, ArcadeControls and the CRT Collective
NOTE: I tried to take some photos but the results weren’t very good – nothing to do with the converter; I can’t use a camera. I have no idea how to do anything other than point and click. But in person the results the GreenAntz provided were so close to indistinguishable from the original RGB signal that I’d be kidding myself if I said one image was better than the other.
Anyway, I could (did) literally circle a calculated "superset" range of values for optimal balance between Pb, Pr and luma to maximise accuracy by minimising transcoding error (there is always some error in analogue transcoding). 
