Regarding dispersal missed out that the idea was they were a gel to slow down the release and dispersal.
I don't disagree. As a former SAR captain I have found the dye to be fantastic however it has a lifespan. The trade off between liquid dispersal and the slow release of a gel limiting the size of the visible area is one for the scientists.
I would guess that if the search area was located in the wrong area then the intervening time between dispersing passive aids and looking for them would defeat both liquids and gels.
Self detaching ELT's and SARSAT beacons are not very common on commercial airliners as they are, generally, not out of contact for as long as this scenario therefore the area of search is normally smaller and more located.