The video seems outdated. There was a nerf to the ballistic shield where it ADS slower, as well as it's movement speed.
The shield only works well in a 1v1 situation. In a 1v2, it's unlikely to win, that is, if both players are focusing on the shield. I myself only use the ballistic shield in Snd and Secure point because players are likely to group up there, making it easier to focus. However, if you have backup, your shield works for you as a massive distraction.
From my experience, players don't like playing the ballistic shield because they cannot get too many kills with it. you will rarely find players using the ballistic shield in TDM and Resource takeover.
Also it doesn't make you immortal. tactical nades still bypasses the shield due to their nature. And to survive a nade blast, you need to look directly at the nade so that you don't take damage, which would mean turning your back to the enemy.
Most of the kills you will get from the ballistic shield is not by the shield or the deagle itself, but by the use of nades and your knife, both of which can work against you from the enemy.
this isn't to say that the shield isn't broken, because it clearly is. Just not overpowerd, but extremely situational. I personally would want a sight attached to the deagle and have the shield a durability meter, where at one point, it will break.