Being a bit of a label queen, and long-term fan of Pilot's disposables, I have now sourced a couple of really nice reusable pens.
There's the dinky Petit, which is clear, so you can see how much ink there is.
And I have black black black (none more black) Metropolitan (or MR, depending on country) medium nib fountain pen and gel rollerball. Because refills are difficult to find, I have taken the precaution of buying a plunger for the FP, only to find to my delight that it had a bladder refill included!
Very happy.