Unless it binds directly to the alsa device (which I think you need to have a rooted phone to access) it still uses audioflinger. So the terrible latencies (into the hundreds of milliseconds) will still be there.
From a user standpoint, it is not terrible, especially considering what it is doing. It is definitely not as real time as a standard phonecall, but if you are not in the same room, you hardly notice it.
It is just on the edge of being bad. You can tell if you talk and the other person talks over you because they didn't yet get to hear that you started talking. This happens more in a faster paced conversation, and you might notice if it you talk with someone across a low quality, high latency connections.
I think it is pretty terrible if you try to use android to synthesize audio. Say if you want it to be used for realtime performance. iOS has about 5ms and Android has 100->300ms. There is a huge difference and makes Android completely useless for that kind of purpose (even fast paced games with sounds effects have this if you notice).