As written, it appears this spell really helps two Bard archetypes with their sonic damage Bardic Performance (Sound Striker and Thundercaller). How? Well, look at the Bardic Performance option for this spell:
Songbird
Source Planar Adventures pg. 44
School conjuration (good); Level arcanist 1, bard 1, cleric/oracle 1, mesmerist 1, paladin 1, psychic 1, skald 1, sorcerer/wizard 1, warpriest 1
Casting
Casting Time 1 swift action
Components S
Effect
Range personal
Target you
Duration 1 round
Description
You conjure uplifting music from the wilds of Elysium, Heaven, or Nirvana to bolster other musical activities.
If you cast songbird during the same round in which you attempt a Perform check, songbird acts as accompaniment and grants a +3 bonus on that Perform check.
If you cast songbird in the same round in which you activate a bardic performance, that round of bardic performance does not count against your total rounds of bardic performance available for the day.
If you cast songbird in the same round in which you cast a spell with the sonic descriptor, that spell’s save DC increases by 1.
If cast in same round (this spell is a Swift action) as activation of bardic performance, no rounds of such are used in that round! It really benefits the Sound Striker as each Weirdword costs a round...it would enable them to go nova for one round at the cost of a swift action and 1st level spell! Might this be why it isn't PFS endorsed?
Sound striker's weird words each specifically cost a round of bardic performance. Having a round of performance not count doesn't change that.
That being said, even if you allowed it it is not all that powerful. It would save you a maximum of 5 rounds of performance (if you were level 20) and make one other spell +1 DC. Hardly something that would break the game.