For the moment this combo is to get that 5% crit chance but mostly is for that +50% crit dmg increase which is event winner gear.
Imagine this rings (Increase Critical Damage 50%) + Earth Shock Trooper (L) armor set (Increase Critical Damage 60%) (but you will have only 100% not 110% because maxium 'Increase Critical Damage' buff is set at 100% from items) + Devastim 15mg (Increase Critical Damage 50%)
So you will have +150% Increase Critical Damage which is event winner gear of course. This is the main purpose of this rings.