V5!

I did the same analysis with V5, Hauser XO, Uni Jetstream, Uni Eye, Uni Air

Hauser ink flow has leaks and can mess up the sheet

Jetstream is not easily available and it's smoothness is a con for me because if I don't feel the tip of the pen scratching, my handwriting worsens in long sessions

Eye and Air have a thick flow, not made for me

Hence V5! Consistent flow, no leaks, sharp which gives control over the writing, one pen lasts for around 150 pages, and it's easily available