Concentration is important for non-casters in that they often tend to be the types to be in combat where it can be broken. Also, importantly, sacrificing your reaction as a melee PC can be very costly. When deciding whether it is good for a class, you have to consider the full opportunity costof casting it, and whether someone else in the party is better situated to cast it.
Silvery Barbs is what we think it is: You'll use it once per LR to try to turn a successful save, attack or (occasionally) abiliy role that matters into a miss - and then give an ally advantage.
You can negate a crit with it: most likely, turning that crit into a miss or non-crit most of the time. Sometimes, however, it will do nothing beneficial for you in terms of the opponent roll - rarely in the crit circumstance but more often in other circumstances.
Then, it will give an ally a boost on their next roll. They don't get to choose the roll - it is the next d20 roll they make.
You can get creative and do thinks like giving a reroll to their perception to see your party assassin and then give the assin advantage on their next roll (which would be initiative). However, about half the time, that will not make any difference for you in the roll, although it can impact how you plan for the results of the roll. So far, my favorite use of this was by a Cleric of Order when a melee ally double moved against a BBEG spellcaster and attacked them to break concentration. The spellcaster was hit, and made their concentration check - we forced an SB reroll, which they made again, and then the melee ally was given advantage on their next roll - which was the free attack granted by the Cleric of Order, who rolled a crit, which dealt 40 damage and forced a failure to that subsequent concentration check.