Google; SMARTFIND G5 GPS (AUTO FLOAT FREE) they cost about £500
MH370 would have been located in minutes and the wreckage found in hours.
You can forget the idea of one of these being of any use. The impact energy of a vessel capsizing is just a little bit less than a 500mph impact with the sea.
The maximum test applied to marine EPIRBs is something like a 20m drop into water or a 1m drop onto a wooden floor.
Fitting marine EPIRBs would simply add to the debris field, that is all.