My wife and I have the Oceanic VT3 computers, which are basically the same computer with a different screen layout. We have not had the computers for very long, but I am happy with them so far. The computer screen is large, which makes it really easy to read. This is the first air integrated computer that I have used and it is a nice feature. It is really convenient to have all of you information in one place.
The transmitter begins sending out a sigal as soon at the tank is turned on. I believe that the range of the transmitter is 6 feet. While gearing up, I have occasionally noticed that the computer has not recognized the signal, but the signal has been picked up by the computer shortly after donning the BCD and tank. You can also prompt the computer to search for a signal from the transmitter if necesary, I have done that a couple times to sync the transmitter and receiver after mounting the BCD/tank.
I have not noticed the computer losing signal yet during a dive. The computer verifies communication with the transmitter regularly, and if it loses signal, it will begin searching for the signal. I am sure that the compters do lose signal occasionally and that is an issue that you should be aware of. I regularly check my gauges and also carry a brass and glass spg just in case the computer loses the signal and cannot re-aquire it.
As with all equipment, things break and malfunction. I have had a mechanical spg fill with water and crap out during a dive, so the threat of losing signal to the tank transmitter does not terrify me. I know approximately what my pressure is at all times, and I dive conservatively. If I no longer have a working pressure gauge, I will end the dive.
The Oceanic VT3 is a nice computer, and you should be able to find a good deal of information on it here if you do a search.
Good luck.
Ryan