Considering the noise (music?) that comes out of them, I would say the "Bling" factor is about 100%.
Kind of like this UniT bench dmm.
It's win win mate, UNI-T has left lots of tool/parts storage space to make the product a must buy
and you could in theory squeeze in a pair of 1 FARAD caps to boost the meter's DC performance, especially in buzzer and diode modes...
OTOH, if you've got a beefy car battery with excellent CCA ability, I can't see what the cap is going to do except perhaps give the battery and alternator a headache
If the battery is under the hood and the amplifier is in the trunk, the cables regardless of size, have resistance and inductance. Placing a capacitor (or even another battery) right next to the amplifier can prevent sags in supply voltage caused by the resistance and inductance. there's also a limit to how large the cables can be and still get them routed to the trunk. It's pretty clear that #10 AWG isn't going to do the job. I don't know what size cable is usually used.
I'm not into audio at any level so I wouldn't know if the capacitors are real or not but I kind of understand what they are intended to do.
Put a scope on the DC input to the amplifier and crank it up. Add the capacitor and see if there is any difference in the trace.
I'm very familiar with auto and hi-fi audio and test gear etc and always understood what these addon caps 'should' do and the sales pitch angle that accompanies such products etc,
but whether that equates to any REAL audio benefits and doesn't burden the vehicle electrical system doing it, is debatable till demonstrated properly and unbiased.
Some products may be legit, and others great retail 'mark up' duds with joules of bling and eye candy factor
I'd like to test a few of these thoroughly under all conditions and see if they trigger or peak on the Stereo BS Meter
but pulled the plug on good car audio for many reasons,
some being that competing with road traffic noise and being aware of danger at high music levels is a no no (lots of speeders and donkeys on ice or medication, and distracted phone junkies on the roads here
)
Even parked somewhere at night doesn't work for long, as the battery gets drained, and one better have a reserve battery in the boot to bail you out to start the engine.
FWIW 'most' partners don't care/can't tell the difference, and in most cases they can't operate a nice system, and happy with simple ON/OFF and Volume controls, so why bother?
I'm happy enough with whatever sound system comes stock in the vehicle, do a check that everything is wired correct and works, no flat battery to think about for a while,
and sounds pretty good with great dynamic music and over compressed Autotuned noise, indie, rap, metal and R+B drivel.
The only way to know if these caps are a worthwhile investment or yet another Auto-Phool wank, is if a member here or Youtuber with test gear and a pumping car rig with a good fresh car battery, and stable alternator to begin with (both items load tested first by an auto electrician if not up to speed with that),
with solid connections and appropriate gauge wiring, wants to set it up and test it
Actually you don't even need to install the sound system in the car for the sake of testing, just have a high powered car audio rig assembled on a garage bench
and hook it up to the car as close as possible, get the right inline fuse/s in place, keeping the wiring as short and thick as possible, ensure all the test gear is isolated or floating and SAFE
and make sure you have a large fan running and the garage door is
WIDE OPEN during the proceedings !