Same-Character Synergies
Shield Master does three things, but they don't really have good synergy with the Rogue's class abilities.
- The shove ability seems like it would have some synergy with Sneak Attack, by making the target prone (which grants advantage to melee attacks), but unfortunately the Sage Advice Compendium requires you to complete the Attack action before doing the shove, so the target will not be prone for the character, only allies.
- The raw bonus to Dexterity saves works, but it's restricted to only single-target effects and Evasion only works with area effects, so there's no synergy there. There is a benefit, but it's not superlative. Unless multi-classing in, a Rogue is proficient in Dexterity saves and likely to have a good Dexterity score. For a character with relatively poor Dexterity saves, it can be a big deal.
- The third benefit, against area affects, is strictly inferior to Evasion, because it requires a Reaction to invoke while Evasion is automatic. They both do the same thing on a successful save (eliminate the damage), while Evasion also has a benefit on a failed save (half damage) that Shield Master does not provide.
None of these have any interaction with Uncanny Dodge, which provides a benefit against incoming attacks (if there's no attack roll, just a save, it's not an attack and Uncanny Dodge doesn't help.
Cross-Character Synergies
Shield Master is stellar in a party with the right blend. I DM for a group with two melee rogues, a paladin with Shield Master, and a sorcerer with Careful Spell. The sorcerer can drop an AoE DEX-save spell on the three of them every round, because Careful Spell can make all three of them auto-pass, the rogues take nothing via Evasion and the paladin can use her Reaction to take nothing via Shield Master.
