With huge experience of writing CSE Mains and qualifying 3 of them, I can say with conviction that Rollerball pens (Pilot V5/V7, Hauser Tech 5, Trimax, Uniball eye micro etc) are better choice for writing Mains compared to ball pen/gel pen. These pens improve legibility, presentation and writing speed.
For 2019 and 2020 Mains, i had used Hauser Tech 5. In earlier Mains, I used Butterflow and Reynolds 045. I really feel bad about coming to know about these Rollerball pens so late in life (All thanks to my vernacular Govt school education where everybody used local ball pens or Reynolds 045 at best; During Engineering, never bothered about writing).
All these Rollerball pens are quite similar in nature and you can choose one as per your convenience. Personally, i prefer Hauser Tech 5.
@indianhuman Hauser Tech5, Trimax & Uniball Eye micro are completely water-proof. Pilot v5/v7 is not 100% water-proof but does not fade too much in case of accidental water spillage; so that is not a concern at all. All these pens are really good and there is very minute difference among them. Write 1-2 tests with each pen and choose the one which suits you more.
@dalpha I had tried all these rollerball pens in test-series and settled for Hauser Tech 5. So i have used only hauser tech 5 in Mains.
@lalitha_shravani I don't find it(Hauser Tech 5) too light on paper. For me, it's completely fine.
