You unlock it at Mastery Rank 15 on that sniper
I've unlock it and it seems to make the difference as can sniper from longer distance where it's harder for the players as they havnt got a massive glint to aim at long distance but I've got a massive glint to aim at so it's make it better for long range as it's the same glint reduce as in the other battlefield games it's not less then the other games it seems to be the same when you put on the reduced glint as someone else in the lobby was using the glint reduced and when i was looking at it its the same glint brightness as all the other battlefield games its not to bright and not to low in brightness its prefect for those who like long range snipering like all the other battlefield games
There's still some things they need to sort with that sniper with the inconsistent with the bullet drop as it's hit and miss it's not consistent and they need to fix the one shot kill to the chest/arm with full heath even from 80mm to 90mm away as I've done multiple one kill shots to chest/arm from 80mm away and then get a hit mark from close range it doesn't make sense so it's something they need to fix