I can't definitively say that the actual sending and receiving messages has ever been anything more than a novelty to our group.
BUT.
The additional data that is transmitted between T2 transmitters as well as the increased range, to me, makes the T2 transmitters a very important piece of the puzzle. We dive DPVs and hunt, a lot, so we inevitably get separated more often than our open water instructors teach is 'allowable' during your first class.
The T2s allow us to know what depth our buddy is at even if they're not in our eyesight. That, plus seeing PSI can help us determine "oh, they're up at 15ft doing a safety stop cause they're almost out of air" vs "they're still here, have plenty of air, likely buried in a lobster hole picking out bugs." I don't know of another transmitter on the market that allows you to read your buddies air integration as well as depth, that far away. Its a nice safety feature for sure.
EDIT: - yea its preset messages, cause the transmitters don't send the full message, they only transmit a small byte of information thats mapped to a pre-set 'set' of messages. Something like:
msg: 4
table of messages
1: Hello
2: Out of air
3: Going up
4: HELP ME
.....
so the T2 would read "4" from the other T2, send it to the watch and the watch would display the pre-configured "HELP ME" on the screen. Something like that.
