I wonder how it would look with PbPr from the ebay decoder since its Y is always 480i no matter the input, but we completely bypass its Y and take only the PbPr which might be okay for 240p signal.
Also, if the decoder has some delay how would the produced error would look like in motion (ie. side scrolling)?
Just by looking at this, I can tell that if the PbPr is not perfectly aligned with Y, the result will be trash.
The colors can lag after luma which will be clearly visible in motion, and shifted horizontally which will look just wrong.
So using a separate PbPr from a digital decoder which adds lag is a big NO, but analog decoder might be okay.
I just noticed that there is a chroma shift in your images which clearly visible in the red drop near the CD letters.
So even analog decoders have some minimal delay which is enough to make the image worse than plain B&W.
Once again, until marqs whips a proper decoder, B&W will do.