Most newly bought iphone the touchid will work like charm even the finger is with a little sweat and still scan and work like charm. After some time the touchid will not longer scan like that and it would need to wipe it totally clean on surface and also finger or else it will not read. This happening to me on both 6 plus and 6s plus.
Related to coating ?

Yeah, first day launch itself hv sufficient of stock. Maybe the reseller felt stock moving slow so they never bother to place much order who know sales pickup afterward and cant cope with the demand.
7 plus gold silver and rose gold are easy to source thou even 128 and 256. Black is the hottie baby this year

I am using ipad charger to charge my phone since iphone 5 till now.

Last year everyone also argue about tsmc or samsung chip haha. Every year should hv a thing to heat up the discussion

Calculate in usd but deduct in ur cc in myr. follow the day it charge the amount exchange rate.