The fancy Taiwanese method link is not working too well for me: it goes to a university news list (not a specific article) and every article fails to load the main image. http://vecg.cs.ucl.ac.uk/Projects/SmartGeometry/halftone_QR/... is a better link.
Nothing of that scans for me. I use "QR & Barcode Scanner" from F-Droid, and all I get is unreproducible numbers as UPC-E codes, not QR.
Tricks like this are often implementation-dependent. Nobody says the scanner must use the center pixel, not an averaging of where the block is supposed to be.
Heck, QR scanners are often sensitive to perspective even when the point of the four eyes is for the program to correct for perspective.
If you remove some QR redundancy, you increase the average scan time for your code. A code that is slower to scan will get scanned less.
Keep QRs boring!
There's definitely a tradeoff somewhere between fanciness and scan-ability though. Say we instead use a transparent mask, so there's both a discernable image in the back and a QR that gets reliably thresholded into the original.
I think it's just a common game to try to use a thing for something other than its intended purpose, especially if that thing can hold an image (QR codes, favicons, etc), because it makes the trick all the more impressive.
How much longer? On the order of seconds or milliseconds?
QR codes are so amazingly robust. More things should be like this!