Sorry for lack of detail in first post.
The pen I am looking for is in essence a more durable, refillable version of the uni ball jetstream 101.
I like the pen a lot, as it is also good for maths as well as writing , unlike a fountain pen. However I am annoyed that it is not refillable, and I really just want a pen for life to stop constantly having to buy a new one every 3-4months.
Are those refills better than the g2?
Yep. They are smoother from the beginning (which I like for my messy and fast writing) and don’t harden. But they used to be ~3€ in Slovenia while the g2 ones are around 1-2€.
Also, the Pentels don’t last as long from my experience.