Thought I would share what $30 gets you if you want to play around with piston filling mechanism.  I ordered these off of Amazon, and they shipped from Pakistan.  Showed up in the mail today.  I have been playing with this pen for a while, so I figured for $30, why not grab the pack.   
   
Overall, for the last few months of running this model, it has been a really good pen.  The nib is decent, it holds a lot of ink, and has been reliable.  If you want to play around, it is worth the little bit of money to play with.

Yep, I am finding I can't kill these things.  Have one that has Iroshizuku Asa-Gao in it.  Was on my desk in the basement for a couple of weeks forgotten about.  Uncapped it and it was writing, no muss, no fuss, just worked.  I think these might be the hidden gem in pens right now, cheap, reliable, piston fillers.  Hard to beat them.

Totally agree. I have a flock. Lovely little pens. Specially like the italic versions

Dollar 717i -- $30 of piston fillers