(Click saver for others, the members:
1. Ms. Tania María Abdo Rocholl Paraguay 2017–2020
2. Mr. Yadh Ben Achour Tunisia 2019-2022
3. Ms. Ilze Brands Kehris Latvia 2017–2020
4. Mr. Christopher Arif Bulkan Guyana 2019-2022
5. Mr. Ahmed Amin Fathalla Egypt 2017–2020
6. Mr. Shuichi Furuya Japan 2019–2022
7. Mr. Christof Heyns South Africa 2017–2020
8. Mr. Hernán Quezada Cabrera Chile 2019–2022
9. Mr. Bamariam Koita Mauritania 2017–2020
10. Ms. Marcia. V. J. Kran Canada 2017–2020
11. Mr. Duncan Laki Muhumuza Uganda 2019–2022
12. Ms. Photini Pazartzis Greece 2019–2022
13. Ms. Vasilka Sancin Slovenia 2019–2022
14. Mr. José Manuel Santos Pais Portugal 2017–2020
15. Mr. Yuval Shany Israel 2013–2020
16. Ms. Hélène Tigroudja France 2019–2022
17. Mr. Gentian Zyberi Albania 2019–2022
18. Mr. Andreas B. Zimmermann Germany 2018–2020 )
Having members in common with the UN does not automatically give it legitimacy. The UN does some good things, and does some things that are to give tinpot third-world dictators a chance to look respectable. The efforts involving the second are fine for trying to nudge countries into being more like the normal world, but should not be given any real authority over anything.
The question is, which camp does the ICC fall into? That question tells how much legitimacy it has as a court. (And I don't know the answer, so I'm not going to give one. All I'm saying is "It's like the UN" doesn't make it legitimate, at all.)