Parker refills are a nightmare. I have tested both the Indian brand and the French brand of QuinkFlow several times, and they are all horrible. Atrocious. I got some Monteverde, Pelikan and Schneier refills and they work well.

If you can get a compatible Monteverde, it is great. Schneier is also very nice, but hybrid. Pelikan has the pelikan blue style, you either love it or hate it. QuinkFlow... ok, whoever says they are fine, send me that legendary "fine" refill I keep hearing about.