Generally speaking, internal speakers in a QRP transceiver, like the µBITx will be inferior. Fragile, rattly and thin sounding, and inefficient. Don Cantrell, ND6T, has written an article about how he dealt with this problem. He incorporates a headphone jack in the speaker with a switch and an associated signal limiter circuit to prevent the RX from damaging his eardrums with loud stations and static bursts.
See his blog page for details.