I've used one that a generous CGN member loaned me last year. I found that like him it didn't make an appreciable difference.
In general, the most serious BR shooters are fastidious in seeking the utmost accuracy but few if any use the G3 gauge. Many more casual shooters will try various methodologies to improve accuracy, but there are no shortcuts that can guarantee improved results other than using lot tested top-quality ammo in a good quality barrel.
Of course shooters can try whatever means they feel will help them wring out the most from their ammo/rifle.
In general, the most serious BR shooters are fastidious in seeking the utmost accuracy but few if any use the G3 gauge. Many more casual shooters will try various methodologies to improve accuracy, but there are no shortcuts that can guarantee improved results other than using lot tested top-quality ammo in a good quality barrel.
Of course shooters can try whatever means they feel will help them wring out the most from their ammo/rifle.