How effective are 20mm sniper rifles really?

[retaxis]

Might be my feed on facebook or whatever but I have been seeing a lot more 20mm sniper rifles recently. Many countries develop them and they are very heavy to carry around. How effective are they really? is it worth moving up from 50BMG to 20mm? Are they a gimmick ?


American 20mm sniper

Serbian 20mm

Houthi home made 20mm


Indian