[Updated July 19th, 2021]
For decades, writers who use Lamy ballpoint pens were limited to refilling with the Lamy M16 proprietary ballpoint cartridge (or M22 if you use the mini-sized Pico or other multi-function pens). When a refill is made by only one manufacturer, in this case Lamy, it limits the number of colors and point sizes available to the writer. Also, if Lamy decides to discontinue a particular refill or increase its price, there is no other compatible option. Yikes! Thankfully, Monteverde introduced an alternative cartridge to fit most Lamy retractable ballpoint pens.