... Parker refills can also be used in Ballograf pens.
I just bought a Ballograf Epoca and have been happy with it. It has a wider barrel, which makes it easier to hold and the quality of the plastic is better than a Parker Jotter. All that for less than $8 bucks.
I was surprised to find that the blue Ballograf refill it came with is archival with the DIN 16554-2 rating, which is similar to Parker's ISO 12757-2 rating. I just did not like the blue color. So, I tried to fit a standard Parker refill in this pen but it is too long and it protrudes from the section. I then disassembled the advancing mechanism by pushing it out the barrel with the clicker. Next, I cut off the small plastic notch that goes into the Ballograf refill's cylindrical end. I also had to trim the Parker refill so it fits nicely. Finally, my Ballograf takes Parker refills. It could also now take Caran D'Ache refills and still take the original Ballograf refill it came with.
Do you know which Ballograf pens (other than the gel version) takes Parker refills right off the box?
Never had a problem using Parker style refills (from Schneider) in the Ballograf pens I use (and never modified anything on them). Just checked it with a Ballograf Rondo and a Parker branded refill (and it did fit correctly). There are even some Bic branded Rondo's and Epoca's that are identical pens and were fitted by Bic with Parker style refills. The Bic Rondo is still available. Ballograf has even a Parker style refill in it's range (see this link) but on it's website it does claim that it fits Rondo, Opus and the Opus2 pens.