• “When using manual braking during taxiing, the auto-brake system will disarm.” INCORRECT. During taxi we only ever use manual braking, therefore, the reference to the use of autobrake during taxi does not make sense.
• “On most aeroplanes the auto-brake system provides a constant deceleration during landing on a dry runway. (ignoring possible transition effects when the system begins to function)” CORRECT. The autobrake system varies the brake pressure to achieve a deceleration rate (about 1.7 m/sec² on the A320 in low autobrake mode). So, when you select “low” autobrake mode in flight, on the landing roll out – it varies the brake pressure to achieve that deceleration rate always. If it is a contaminated runway and it can’t achieve that rate, fundamentally, it will just achieve what it can achieve.
• “When a low auto-brake setting is used during landing use of reverse will not influence the brake temperature.” INCORRECT. It obviously will, the autobrake varies the brake pressure to achieve a constant deceleration, so therefore, if you’re using thrust reversers, some of that energy (to dissipate speed to achieve a certain deceleration rate) is being supplied by the use of thrust reversers – therefore, they reduce the amount of brake pressure which has to be applied on the brakes => brake temperature will reduce as a result of using reversers.
• “When the auto-brake system is inoperative, in general take-off is not allowed, because maximum manual braking does not achieve the same deceleration as the auto-brake system in the RTO mode.” INCORRECT. We would say that this is a bit type specific, as take-off is usually allowed with autobrake inoperative, however it is inputted as a factor which increases the ASDR. The deceleration rate should be the same, but pilots do take longer to apply the brakes than the RTO system does.

=> Fundamentally, if autobrake is in rejected take off RTO mode and you reject the take off => then the braking will be maximum possible braking, which is exactly the same as if you press on the pedals maximum. The same amount of pressure is accomplished, the only benefit of autobrake is that the braking happens immediately, you do not have to wait for a pilot to respond to it. And, therefore, the braking distance without an autobrake is longer => because of the reaction time.
BOTTOM LINE: same deceleration is accomplished, stopping distance in manual braking is greater due to the reaction time.