Modern demonstrators are interesting, because they show the pen's filling system and the ink's colour. However, as soon as you consider wearing one, or using it in front of someone, safety is the first question that comes to mind. Seeing floating ink triggers a bit of anxiety. To the experienced user, the anxiety may go away, but is annoying when people step back in a sudden fright, away from your pen, and thus away from you. Let assume that you are confident with that situation, enough to bother only about ink capacity. Then comes the question of what filler you really want to see. Both the aerometric and the cartridge are a no-no; you just do not want to see them. The c/c is slightly better; you see the ink, but then, why seeing the void of that double barrel? Then comes the piston filler; no double barrel, better capacity, but there is still a lot of void on top of the piston. A lot of void, to be fair. Then comes the eyedropper. At last, the barrel is fed to maximum capacity, and the ink stares back at you. Being a modern demonstrator, it is also safe, and then, having made the roundtrip in the history of filling systems, with a thumb on one's cheeck, one asks: why did they drop it in the first place? And the next question is: who else is selling modern (safe) eyedroppers nowadays?
Luca