If enabled, I'd be curious to see how well it ends up working. When Ken (BI developer) enabled two-way audio on the 1831C-PIR, it wasn't too useful for me because it wasn't full-duplex. To talk to the camera in the BI smartphone app, I had to toggle the MIC button on, say what I was going to say, then toggle the MIC button off. While the MIC button was on, audio coming from the camera was muted, so if the person on the far end said anything I couldn't hear it.
Using the Dahua app to two-way talk to the camera was a better experience for me... I could hear from the camera at the same time I was talking to it (i.e. more of a full-duplex experience).
I don't understand how two-way talk should actually work, so I don't know if BI is trailing in that area, or maybe BI is normal and the Dahua app is doing some magic.