Jay, you are correct, the brake PAD indicator is only to measure /indicate when the inboard brake pad has worn down to the sensor, causing it to send a message to the light to come on!
I like the Zimmerman rotors, they are pretty well built, and made with good quality steel. Ive used really cheap brands before, but have invariably been disappointed.
Rotor thickness is dependant on pad aggressiveness, a long wearing pad will wear a rotor faster than a softer one. ( which is cheaper to replace, a rotor or a set of pads!?)
Ive developed warped rotors after a nice mountain decent, (nice and hot!) and drove through about 2 inches of standing water (nice and cold!) the result was almost an instantaneous rotor warp! (a cheaper no name brand)
ive learned it makes no sense to skimp on cheap brakes!

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2003 X5 3.0i (02/2003) sport package, Sapphire black metallic / Black Dakota Sport seats. compass mirror retrofit, trailer hitch retrofit, Prodigy P2 trailer brake controller installed, PDC retrofit, Lumbar support retrofit. heated rear seats retrofitted. Running boards retrofitted and subwoofer install in progress. 4.8is Brakes installed front and back. Bluetooth TCU installed, Rear Fog lights installed. Retrofitted reclining rear seat backs.