Hmm.
Taking 8th in Bard gets me 6+ Int skills, one additional 3rd level spell known, one extra spell slot for 2nd and 3rd, and bumps Inspire Courage to +2.
Taking that same level in Master of Masks gets me 4+Int skills, a 2 point bump in Fort and Ref saves, and two masks.
The Angel mask gives me Feather Fall at will, and 5 rounds of Fly per day.
The Archmage mask gives me 4 1st level spells a day, Mage Armor, True Strike, Reduce Person, and Magic Missile. Not bad.
The Assassin mask gives me a dice of Sneak Attack, and a +1 to Hide and Move Silent. Not bad.
The Demon mask gives me a Summon Monster III once pr day, to summon evil creatures, though they're only around for one round per Master of Masks level, so it's kind of weak.
The Dragon mask gives a fiery breath weapon of 2 D8 damage three times a day. Not great, but okay.
The Gladiator mask gives +1 to hit and damage, and grants proficiency in all martial and exotic weapons. If your Bard is any kind of martial build, this one is a must have.
The High Priest mask gives 4 1st level spells a day: bless, cure light wounds, protection from evil, and sanctuary. Not bad.
There are more. No mask is overly powerful, but they can add sharply to the character's versatility, and that's really the hallmark of the Bard.
So I'm not at all sure that it's weaker than another Bard level.