My Postman brought me this little oddity today ...
Vintage Mongoose?
What you do is twist the bottom and the handle rotates 45 degrees, the mouth drops open and you can load a blade in ... proprietary, naturally, but injector blades fit and shave pretty well from a quick go this evening ...
... the presentation looks scary and the gap ludicrous, but it does actually shave pretty smoothly so long as you go with the contour of the top cap. The blade can be brought right up to the guard and clamped shut, tight ... but it seems to work better further back from the guard.
Oh, it's a 'Leslie' by the way.