I have two of them, complete, in working order. Very interesting razors. I have been meaning to put them up on fleabay since I never use them and nobody gets to admire them, but I just cant seem to part with them just yet. Same with my Rolls sets and my several other hoe handle wedge sets by various makers. They are a fascinating evolutionary dead end between the ordinary straight razor and the disposable bladed safety razor.
They can all be made to shave nicely, but the Darwin and Rolls and other gimmicked razors that are honed and stropped in the case, actually shave MUCH better when the blade is taken out and honed like a straight razor. I am particularly partial to my Heljestrand set but the Kampfe/Star sets are very nice, too. Oh, and my Henckels set, that one is a particularly fine shaver.
Anyway, basically what you have is a hoe handled wedge blade safety razor, designed to be stropped using the mechanism in the case. The self stroppers like the Darwin and the Rolls were considered luxury items in their day. Many were given as gifts but never or seldom used, and never tossed due to just being so darn clever. Darwins are much less common than Rolls razors. Rolls were still made well into the 50's though quality IMHO fell off a bit with later models.
Even though they are referred to as wedge blades, they are actually hollowground. They are called wedge blades to differentiate them from the later wafer blades which were thinner and had no spine, or else a pressed on spine.
As you can imagine, blades are harder to come by than handles, for this type of razor. There are a lot of orphan handles and cases out there in the wild, showing up on fleabay a lot, with no blades, or one blade in poor condition. Don't bite. A waste of your money. If you find yourself stuck with one, you can make a blade out of a Gold Dollar straight, though it is an awful lot of work, especially if it takes you as a beginner a dozen attempts to get it right.