guys... voltage stabiliser is NOT a thingy to stabiliser voltage ler. The thingy to stabilise voltage is a voltage regulator... and that can be found in your alternator.
In saying, in order to produce a correct voltage, ampere, watt ... watever your alternator must be in good condition. There are carbon bushing which tear and wear off over the years hence resulting in low yield and instability.
Furthermore, your grounding cable must also be in good condition. After year of heat, grim, dust, salt, rust mouse, rat... etc. conditioning, it is a good idea to check on those. Alternatively, you can buy those aftermarket ones but in my humble opinion, it makes your engine looks like a broken down old spidey web with wires running along everywhere. Go get one of those thick welding cables and sub. it with your main ground cable below the engine, and u will find some effect to your car.
The blue box thing does do something to the electricity that is passing in your car. Some people say, better FC, engine smoother, gear shift nicer, brighter headlights, electrifying back seat experience etc etc. especially in older car. Maybe it does perhaps some truth to it as it last for a few weeks and then that's it. (I tihnk that the same principle that goes to all petrolheads. HHAAHAHAH.. yeah... i for I too.) Psychologically effect, maybe? Well that's x-files.
For me, I still have it in my battery tray as it looks nice with a bluish glow whenever I open my booth. And chicks goes, "Ooooo... bimmer so canggeh one!" Not bad for a Rm150+ decorative item + chicku magnet + conversation starter.