Full Reverse in flight is both safe and legal last time i looked in the flight manual, for the Cresco (Although i'd recommend you be shown how to do it, you could overspeed the gear box with the incorrect technique ).
Did some parachuting in Cairns in a Cresco a few years ago, reverse is a very handy tool for descent when operation at the DZ ( i.e. an airport ), 7000 plus ROD at 120-130 KIAS.
Infact, with tandems under a drogue, you could descend faster than them.
Aircraft such as the Porter and C208 have previously been allowed to operate like this, unfortunately a few in-experienced pilots did it too close to the ground and killed themselves, therefore the relevant flight manuals were changed.