I have two. I have seen four, 2 button fillers, a piston filler, and a lever filler. If anyone has more information I'd be glad to hear it. This HR pen is the same size a Senior Duofold. And a little button filler.
Both cool pens, i like the bottom one. Look German, and the top Duofold look-alike looks to be possibly Italian or French by design. They are Belgium pens... And here are some ink bottles to match.
Rather nice pens!! Haven't come across these before but "Brussels" on the nib leaves no doubt as to where they come from, they have "quality" written all over them so look forward to learning more about these.