Thrust reversers are wonderful devices for making noise, but they are not very efficient in stopping aircraft on dry runways when the brakes and spoilers are working.
For certification purposes they are not even considered in either the aborted takeoff calculations or the landing calculation.
So the next time that you are sitting on an aircraft where the crew decided only to use partial or no thrust reverse, dont panic, you will still safely stop within the planned landing distance.
Mutt.