I've seen someone trying to sell them on eBay before from Japan for a couple hundred bucks a piece.
I really like that long handled version of the portable. He sold this Feather Open Comb a while back. The design of the bottom plate reminds me of a Rotbart.
I inquired about these razors a while back, same seller from Japan, Asked him a few ?'s on why such a high price, He wrote back and sounded offended, Not finding any info on this amd asking him for proof of authenticity and he got offended it threw up some Serious Red Flags.
Play it safe and call Feather and have them confirm that they did carry such a razor a while back if you cant get any confirmation from feather stay away, just my Two Cents.
I wouldn't expect Feather products from the 50's and 60's to be well documented on the internet. It's certainly possible that there just isn't much info on them. One could certainly verify directly with Feather.my guess is they are either prototypes or ones that never saw the market.