The eyedropper filler was never a successful solution and there was a scramble to come up with a better arrangement, which Sheaffer won. Their lever filler depended on a pin drilled through the barrel, a system that was not entirely satisfactory and which they dropped later.
Nonetheless it was the first working self filler of the latex kind and Sheaffer guarded their intellectual property fiercely. They produced superb pens which have survived in large numbers and continue as first class writing instruments today.
Due to Sheaffer’s litigiousness other pen-makers continued to try to find another way, most based on the pressure bar means of deflating the latex sac. Some of these solutions appear eccentric to us now, thumb fillers, matchstick fillers, clip fillers and so on through an almost innumerable list of clever ideas. Odd they may appear now but most worked, and worked well. The crescent filler made by Conklin was very successful. It may even have been a better filling system than the lever filler in some respects – it couldn’t roll of the desk, for one thing – and it was adopted by the Japanese.
Seeing the sale of Sheaffers, several companies concentrated on making a lever filler that was sufficiently different not to have their makers hauled into court by Sheaffer. Watermans box lever was very popular though it has proved fragile in later years. It was copied by Conway Stewart, whether or not by license is unrecorded. Snapfil developed another type of lever filler and beyond that the door opened to everyone. Companies like De La Rue and Wyvern had their own versions of the box lever which proved more durable than Watermans.
Though it seems an imperfect method of filling a pen, the lever filler was adopted generally. Other filling systems sprang up too but that’s for another time.