Regarding voice call quality, I have observed that during a regular phone call, SoSIM network is switching from LTE mode to 3G and 2G mode and then it switches back again to LTE mode after call is over. This potentially disconnects data for a while. This switching back and forth is less pleasant experience and might require activating VoLTE pack.
Also I would agree that network is bit weaker than Birdie. But again for $$ I am paying, it's fine !