Thanks
The one I'm interested in is the one that takes a de Blade (half)
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In my view, that's an aggressive razor. It also requires a certain amount of work to load and unload the halved blades, and break off the blade tabs. The video makes tab removal optional, but I find it essential to do. It is also possible to cut them off with sharp scissors before inserting the blade. Positioning of the blade has to be precise and even, and of course it's done entirely by hand and eye, without locating posts, pins etc. that other DE and SE razors have. Troubles will arise if the blade protrudes unevenly side to side, and failing to get the blade in right so that the cutting edge is parallel gives an undesirable quasi-slant effect.
Whichever way things are done, there is more close quarters contact with a very flexible (as opposed to Gem and AC types) DE blade, which isn't just sharp on the cutting edge, but can also be on the broken edge, than ever with a conventional DE razor. Considerable care is called for.
This is the Rocnel video:-
Rocnel SE-P
It's very well made, and a clever design, with the only two parts being the one-piece head and the handle. I continue to find the way it holds the blade so firmly, absolutely fascinating and slightly miraculous. It doesn't handle or work like a DE razor with half the head missing, and I struggle to think of another to compare it with. They were originally only SB, but then they also produced an OC version. The SB is quite enough of a handful for me, and I think I'd find the OC a step too far.
I personally don't think that there's any gain whatsoever in having the sharp edge corners of the blade exposed at the sides (as with the Gem razor), as no-one angles a razor over to make the blade corner contact the face (at least, not on purpose). Both might be better if the heads were fractionally wider, and overhung the blade.
Rocnel had a flurry of producing novel razors about 2-3 years ago, but they don't seem to be quite as prominent as they were. I'm not sure where you'd plan to get one of these from, but someone in Finland was selling them, as was Extrashaving in Turkey. They do seem to have become scarcer, and it's not clear to me whether Rocnel are still making them.