Underseat subs... Well... I am using an underseat that is branded (I suppose) and i just installed a ported box subwoofer in myvi for half the price of the underseat sub alone (Exclude install, wiring and workmanship)... To be honest, it worked better, responded better and sounded better than the underseat and is richer in most ways... Now i finally understand why so many ICE sifus keep emphasising on using a boot sub rather than underseats... If you want very good bass in a car, go for the subs that fit in your boot... If you travel a lot and need the boot, then your only option is to fit a pair of underseats to get a solid bass thump

I bought Infinity Basslink SM 8" from xciteaudio.com
RMS 125 watts and built in class D amp (written on the box but who am I to judge)
Has good bass in my opinion but maybe not boomy enough for me. Maybe if you frequently listen to soft music and those usual pop or jazz genres then it would work wonders since it is mainly focused on SQ.

The other sub i bought is a cap ayam brand audioquart (Huricane series if not wrong) and also normal audioquart 2 channel amp to power it. Add in installation and sub box and wiring (did not change HU and previously installed Hi/Lo converter for the underseat so no need to pay for another one), only cost me 550. Sub rms is said to be 500 at 4 ohms but i'm not so sure and the 2 channel amp i am not sure how much power, but the box did say 180W x 2 bridged at 4 ohms so that's that.

Quality wise, the Infinity takes it all since it has nice clarity and a clearer bass thump which costed 1.1k alone exclude installation. But since i just wanted boomy bass, the cap ayam fitted the bill. Just not sure how long the amp will last

Yep... Forgive me for being a basshead...

Why? You wan ah hahaha
Still hooked inside my myvi along with the cap ayam boot sub hahaha

Not planning to hahahaha

Actually almost all of them perform the same since they are sealed compact subs
The difference maybe on the build quality and clarity of bass instead of loudness since they are predominantly for SQ
If you require rumbling bass, go for ported box sub in the boot (slightly pricier since all of the components are sold separately but has more bang for your buck)
Those underseats, maybe if you like to listen to chinese genres, or modern songs instead of EDM, bassy songs, they do the job, even the cap ayams (MBQ, American Sound, etc.)

Underseat would do the job fine but it won't be cheap tho if you want high quality stuff
My installer recommends adding amp to drive door speakers for a richer sound and also you will notice better bass notes but it all also depends on your HU
Btw what car are you planning on installing it into? I heard my installer say that different cars have different type of bass response since the cabin space plays a major factor in how bass response sound to our ears.

Well what I can say is that you've purchased a bad sub... The rubbery thing is the speaker rubber surround or foam surround. The only reason i can think of why it turn to this is because its very old and was not kept well by the seller.
Unfortunately, you cant really repair these underseat subs since their speakers are not conventional aftermarket speakers, they are custom built to fit the sub only from what i know.
Now what you can do is see whether Lazada or the seller got give you warranty or not so you can make an exchange.
If not and you still wish to just own an underseat, go to xciteaudio.com and look for Kevin, they sell some high quality stuff over there and mine is still working until today (installed like half a year ago) and its able to work quite hard and boom quite loud. Plus they give you one year warranty as well.
Merry Xmas and Happy New Year