Pre-made PCB to drop: 12V->6V
It states on the front page that efficiency is 93%. It also states that you can use it to supply 3A. That means an 18 watt load if you have the output set for 6 volts. A 7% "inefficiency" is about 1.3 watts and given its small size it will get quite warm.

If you have a genuine 30mA flowing into it from the incoming 12V supply then the actual no-load power is only 0.36 watts so, my advice is to expect it to get a bit warmer under full load conditions and make sure you can provide natural convection to remove heat (see graph at top of page 5 of data sheet).