That appears to be because they are the sharpest
Gillette blade
on the initial shave based on the aforementioned linked testing page.
Another "sleeper" by
Gillette is the rarely encountered red & black box
Stainless:
https://www.razorbladesclub.com/razorblades/#product_8679
Here's a in depth look at the
Rubie:
https://www.razorbladesclub.com/gillette-rubie-platinum-plus-double-edge-razor-blades/
Notice that the hone angle is 15.6° – 17° as opposed to the
Silver Blue angle of 14.9° – 15.5°. They measure the
Astra SP at 16.3° – 16.8° and the
Feather Hi-Stainless at 13.8° – 15° respectively. I find this fascinating as obviously they are doing this for a valid reason which appears to be some complex formula based upon geographical location equating beard type plus most likely a host of other factors. I harken back to the fellow on another forum who seemed to either be a
Gillette employee or privy to insider info as he mentioned this a few years back. He doesn't post there anymore as the assortment of knuckleheads over there only wanted to dispute everything he said.
Too bad as he was certainly a "taproot" of knowledge. He stated, albeit thinly veiled, that the
Silver Blue was a new incarnation of the discontinued Russian
7 O'Clock Super Platinum (blue box, not black Indian) when people were paying outlandish prices to Russkie "scalpers" on
Ebay.