From experience; USSD NI (Network Initiated) dialogues differ from their  MO (Mobile  Originating) counterparts in that the former come with the annoying "Spurious" displays to the handset. i.e In between the requests & responses, there are definite pauses (Handset goes completely blank).

The MO dialogues have better user experience. Most handsets will show some "processing" indicator etc. Would be nice to see if you hacked that bit :)