The pre-mixed DJ service is where the band put on a bespoke playlist (you can request up to 30 songs in advance for this) through the PA before and after their live sets. We do this at most events and it works great - the volume of the music would be the same as if you had a DJ.
If you upgrade to the live DJ service, you can still send over preferences in advance, but you will also have a band member selecting and mixing tracks live on the night, as well as taking requests. The DJ will be happy to make important announcements but they will not talk constantly over or between tracks (that's just not our style!). We also think it's important to say that the DJ won't have a separate DJ booth - they will set up in an appropriate space (ideally to the side of the stage) and the PA/lighting will be the same as what is being used by the band.