Love this set of pens! They're so cute and actually have a really great ink lifespan. I use them at work, in a deli/bakery, and one pen is used to write about 300 price labels every day, and they last about 4-5 solid months. Customers comment on the pens all the time, and some even think it's real somehow??
The ink cartridge inside is slightly longer than that of a normal pen, so you can't simply swap out cartridges when the ink runs out and you want to keep using the cute pen. I did however once fill the ice cream section with a bit of tin foil to fill up the empty space, and then I was able to use a normal size ink cartridge without it getting pressed back up into the pen when trying to write.