I don't think soundproofing solve rattling noise for most case unless u made it specifically to solve the rattling part.

for general soundproofing with mat I think it depends on what type of car your are driving too, some car that came with good insulation will not make huge different with these mat.

Like example if u apply these mat on any Perodua you may notice huge difference because their car not well insulated.

I had 2mm mat installed on my Persona VVT all 4 doors + firewall, I do notice the engine noise is slightly quieter, noise from outside also slightly reduced because originally Persona already have mat on door but smaller pieces, more obvious is when driving high speed above 110km/h noise from outside is reduced, like your sense of speed based on sound got reduced. But does that makes my ride feel like sub RM150k car level of soundproof? No... My X50 still way quieter compared to Persona although I did not do any additional soundproof on the X50

For X50 it is already pretty quiet to begin with, if I were to insulate I will focus how to reduce tire noise.

If I frequently drive above 100km/h I would also consider insulate all 4 doors because of what I have experience with my Persona I think high speed ride will be quieter.

Also soundproofing is a never ending journey, when u insulated certain noise, the other noise become more apparent, like my previous Persona ride, I felt tire noise become more annoying after the soundproofing.

Would installer cause rattling or not this is quite subject to installer, the good one will probably try to tape any dangling stuff like wire to reduce unnecessary noise, the problem with rattling is quite subjective, loud and consistent rattling may be easy to spot and fix, the problematic one are those that appear randomly because it is hard for you to replicate that noise to installer to fix.