Not for sure, thats what the testing is going for.
IMO (In MY opinion) the voltage boosters are for those with a stock alternator needing a little bit more. I asked around, and they do really work.
If you want more...real time, with no clip on's as I call them, then change the coil windings inside the alternator.
With the piggy back dual rectifier set up...many use it for a back up and a better way of heat distribution from them, as the second one is exposed out side the case. many will also remove the internal one all together, and remote mount them outside the case, complete with a 12V fan running on them. If thats the case, either their design of alternator is a bad one, or they need to modify the internal fan with in to get more air flow across it. (IMO)
The one I'm working on is a piggy back dual set up, so to say.
~F~