Nice to hear you made it to the end (and found that little secret hiding, hehe). As for pushing versus pulling the flies, during testing, we found that it is possible to beat each level by just pulling the flies, but its a struggle. And I appreciate the feedback on being a bit repetitive: I'll keep that in mind when designing levels and environments going forward!
And hey, if you liked the music, heres a Beepbox link: https://www.beepbox.co/player/#song=8n31s6k0l00e0vt2nm0a7g0wj0ai0r1o3230T0v1L4u1...