Hi Olendirk,
The autobrake system is quite helpful. Ie both on landing and if you need to reject the T/O. We always use it in our daily ops
If you are rejecting the T/O. The autobrake system when armed starts braking when the the thrust levers are retarded to idle and wheel speed is greater or equal to 90kts. The Auto brake in this case applies the equivalent of full manual braking force.
On landing. the autobrake provides 4 selectable rates of deceleration. 1,2,3 or MAX. (btw MAX is less than full manual braking).
Braking begins when the thrust levers are reduced to idle and main wheel spin up of around 60kts occurs.
Autobrake doesn't directly give or receive a signal from the reverse thrust. It does however maintain (or try to maintain) the selected deceleration rate. so by selecting reverse thrust you are in effect helping the aircraft to maintain the selected deceleration rate with less braking.
I hope that helps a bit.