[DeepThought]

I think that the transmitter is actually a disadvantage in most cases. The problem is that except when used to extend cover when viz is low and the diver doesn't have a line/float line, it will make poeple depend on this device as the first line of defence while the buddy will have the liberty to do something else rather than proper safety. I can't understand why someone who can actually get a buddy would not dive with proper safety procedure: one down, one up and watching. Yes, even for spearing! And if one does that, there is not much a transmitter can add, if the transmitter is activated it means the diver is on his way up already. The person would probably be floating before one could meet him and aid with a mouthblock in mid ascent. Not to mention that might infact slow the ascent.
Well, actually I can understand why one would not use a buddy if having one, it is overconfidence that is causing that. I guess that person never blacked out unexpectedly or aided such a case or didn't learn from this experience.
It happened quite a lot, it can happen to ANYONE and the next time might be the last!
This vest should be used as a redundancy, have it there and always pretend it doesn't exist.