The size of ink bottles.
Ink is probably the cheapest part of this fountain pen hobby for most of us.
Comparing prices is difficult and a subject of itself(nicer and more expensive bottles, and huge differences in bottle sizes). But a cheap ink is around $5 and I haven’t found a single bottle priced much higher than $40 (I checked Goulet and JetPens).
You will spend a lot more on the notebooks you need to fill in order to use the ink, than on the ink itself.
If you are the kind of person that only uses one colour, and order another identical bottle when you run out, then larger bottles are probably a good thing. But it might not be if you are like me.
I’m usually sick of a colour, with a very few exceptions, after I have used somewhere between 1/3 and 1/2 of a 50ml bottle. If you have read this site for a while, you probably get that I’m a minimalist. I don’t like having a lot of stuff collecting dust. I complete a notebook before I start the next, and I don’t keep a lot of spares. Because I don’t like it.
What I want is smaller ink bottles. Because I don’t care if a bottle cost me 5, 10 or 30 dollars; and I don’t care if they are 15ml or 50ml, because I’ll spend a hell of a lot more on notebooks than ink. My desire for using different inks are a lot larger than my need for getting as much ink as possible for my money.
I write a lot, and I think I can complete somewhere between two and three bottles a year, probably closer to two. Which means I have to put some serious limitations on how much ink I order to avoid being in the “I have more ink than I can use before I die” situation. But I could buy a hell of a lot more, and try a hell of a lot more inks, if the bottle sizes were like a third of what they are today.
I assume that the reason there is so much ink in each bottle has to do with the fact that the amount of ink isn’t what makes it expensive. I assume they feel like they want to give as much value as possible to their customers. And that’s good, I just want the option to also get it in a smaller bottle.