The thread Is interesting but I suppose you would have to remove the blade and flip it over to sharpen both sides of of the edge Are these rare? as I checked ebay to see if I could get one and I get no results for my search
It will require a bit more searching than eBay. They are out there, keep an eye out on eBay too; you never know when they'll show up.
I wouldn't say that they are rare, exactly. Unless you run across the one with the bakelite handle...that one is rare. They are definitely not common either. I'd say one turns up on the net about once a month or so. I've seen four or five this year, but I haven't looked in several months. Expect to pay $35 to $40, though they really ought to sell for much more than that, considering how well they shave. Ideally, a modern razor manufacturer should copy the design, with or without the sharpening feature, it's still an awesome bit of kit.
