Hi there,

As I am one of the stunt divers (yes, I died twice but survived in one of my 3 characters ; )
and I just became member of this fine forum I'll try to answer some of the questions.

There were 9 custom made Megs used in the movie. Their canisters are smaller than regular Meg BUT theu hold the same amount of Sofnolime as the regular. 6lbs. There is just less empty space. The regular size will accomodate CIS scrubber, the movie canister will not. There is no problem with purchasing the bigger scrubber for movie Meg if needed.
Advantage of the smaller movie canister - the whole rig fits in carry on luggage! I know - I flew with mine to Romania for the shoot.

Yes, originally the movie Megs were equipped with ExtendAir cartridges - we used them in shallow water while shooting the movie in studios in Romania.
Before we continued the shoot in real caves in Mexico we had Leon to make us granular Sofnolime canisters. The ExtedAirs were easy to overbreath during the seriously rigorous work while shooting special effects.

The scooters used in the movie were DiveRite Arrows.

The stunt divers team were all experienced cave divers also skilled in underwater lighting, rigging, and multiple other skills.
I've mentioned some of the team in my post about deep Meg diving into the Miocene.
The stunt divers were Jill Heinerth, Brian Kakuk, Andreas Matthes, Mark Meadows, Jakub Rehacek, Joel Tower and myself Jitka Hyniova.

The Cave movie Megs performed flawlessly in some of the harshest conditions, we spent over 2500 hours underwater (ccr and oc combined) during the 11 week shoot.

Cheers, jitka