For one thing, Moser's Blessed Circle offers an increased Block Rate, which certain shields don't offer. However, most notable is the boost to Resistances that Moser's Blessed Cricle has. Most small shields, although they have high chances of blocking, do not have the resistances that Moser's Blessed Circle does.
Moser's Blessed Circle is socketed. Therefore, a character can have a variety of customizations with it. One could add perfect Diamonds to it, further increasing its resistances or customize it with other ways via Runes, Jewels, and other gems.
Moser's Blessed Circle is a versatile shield- certainly not specific to classes, its sockets make it customizable to whatever its user wants.
Moser's Blessed Circle
Required Level: 31
Required Strength: 53
Chance to Block: