I've only had bad experiences with Parker pens and refills, they just don't flow and fill the line as nicely and constantly as Pilot Hi-Tec and other Pilot pens.
I paid more than 20€ for a Parker pen with refills and it was worse than a 3€ Pilot V5 Hi-Tecpoint (which is my current favourite, I have it in black, red, green, blue and pink colours).
Most of the best pens refills are made by japanese companies (eg. Pilot, Zebra, Uni-ball, etc.) and Parker style is nonexistant in that country. If you look at any "top XX best pens" lists online, the vast majority is not avaible in Parker. And when they are, they usually have fewer color and size options.
It's very disapointing to see brand new nice pen designs that only support Parker refills.
Pilot V5 Hi-Tecpoint has been my favourite for the last ~20 years. I'm not a heavy user, so one pen lasts for years as an added bonus.
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.
Ive had good luck with ‘Monteverde Capless Gel Ballpoint’ refills for my Rotring 600s.