It will usually void the warranty. Not recommended.

10% also very dark, confirm JPJ or police will stop u in roadblock. Without warranty, ggwp burn ur money for nothing.

Ni mesti first time buy car even car bought by parents

Add so dark tint for what? You'll be endangering everyone during night time.

You should prioritise UV reduction than light reduction

If light too bright, wear sunglasses

u first time tint or what?

two layer tint is a bit bodo.
distorts vision + puts stress on your power windows + voids old film warranty.

I would say that it depends on whats your purpose of applying the second tint.

either

1) heat reduction
2) increase the 'darkness'

I've done it with both purpose. My findings as below.

1) Heat reduction increases - proven
2) darkness level increases - proven

However the following are the drawbacks

1) It voids the warranty of the 1st layer
2) It degrades the quality of the 1st tint - bubbles up faster
3) Usually installer will not warranty 2nd layer
4) Once the 1st layer degrades, the 2nd layer will degrade too

Ultimately, its your call.

Coz its an ultimate matter of one word = COSTS

1) If the layers degrade, u have to change both
2) Potential issue with the authorities coz when its dark...its obvious that you have over tinted

But I would suggest NOT to double tint the main windscreen. It effects your vision greatly.

Hope this helps.