My understanding with the ABN is that like DEL mentions above - it fakes out the communication and the kissoff so the Panel wouldn't know to try a backup method should the primary fail. At least in using native TCP/IP, the panel knows if communication succeeded or not; and upon failure can use the backup method. That right there means everything to me. Also, I don't want to worry about minutes - so I prefer the AlarmRelay method where the $12 covers the cell service - so I don't care if it checks in every 10 minutes as long as i'm not taking the hit personally.
Alarm relay is like using a DACT you dont know if you have a connection or not until you test or use it if it is not constantly polling. For $12 a month I dont think you are constantly polling but you can ask them. Would you and the CS know that the transmitter is dead or unable to make the call to the central station until its to late? It all depends on which radio you use as Alarm Relay recomends about 7 and they all have different limitations. Some of those models are also tricking the panels DACT into thinking it is connected to a phone line no different then the ABN (possibly worse if you are not polling to the CS).