"Take off at your discretion" is the most useless piece of non-information that contributes nothing to safety or situational awareness (IMHO). I mean what is it actually telling the pilot? Even an A/G controller will tell you if there is "No reported traffic".
Here is a very interesting link to a
document by EGAST on RT phraseology. Look on Page 21 - the suggested FISO phraseology here is far more useful:
Pilot: D-CD, ready for departure
FISO: D-CD, no reported traffic, runway 06 right hand circuit free for
departure, wind 090 degrees 8 knots, report airborne
Pilot: Runway 06 right hand circuit free for departure, wilco, D-CD