To add to the PenBBS and Wing Sungs already suggested, I would mention the Caliarts Ego.
Piston Filler, about 2 mls, cap seals with an o-ring and is transparent, so any leaks are visible before you open it.
Comes with a Pilot 78g compatible nib, so if you aren't happy with the nib, you can replace it.
I have been using mine as an everyday carry for a couple of months now, and haven't had a skerrick of a problem.
+1 here, and I use a Ego-2 solid Sky Blue color vaersin as my EDC , actually just finish the ink yesterday. I have found that the solid color material more robust than the Demo. I have measure it to give tha the pen hold roughly 2.15 ml when fully filled