You might lose more MM than 5 based on the math on the wiki (just may need to check that math), but if you're trained to 3x in shield use with the shield mastery, then maybe. Also, it's sort of a moot point in this thread because not only can bards not train in all the fancy shield maneuvers, they can't train shielded brawler either. Shielded Brawler was brought up as an argument that only Rogues/Paladins/Warriors benefit from UAC because they're the only professions that can use Shielded Brawler - which is ultimately false.
The only people who benefit from Shielded Brawler are open UAC fighters that can train shield use sufficiently to master all the various mitigating skills. Which is just warriors, and maybe paladins (though 2x in shield use limits how much a paladin can mitigate the MM penalty).