SiftekharNo, you don't. The pen actually comes with a squeeze converter that's pretty much the same as the CON-20, so you can use that if you don't want to use ink cartridges.
SiftekharThe included squeeze converter and the CON-20 hold nearly the same amount of ink as a cartridge (0.8-1.0ml). The CON-50 is a piston converter and holds about 0.5-0.6ml. The advantage of the CON-50 is that it enables you to see how much ink is remaining. You can't do that (by sight) with the included converter or the CON-20. Alternatively, you could just refill empty cartridges using a syringe and a blunt needle.
I have used all of these methods/converters except for the CON-20 and have had no problems .
I have used all of these methods/converters except for the CON-20 and have had no problems .