This drill I did not do, mainly because ripping the regulator will probably break the adapter which keeps the regulator attached to the mask. But when it's life and death situation, I am willing to do it. It will come out, the adapter is attached to the regulator like the mouthpiece and secured with a zip tie. On the other side, I performed the standard drills for a ffm (ffm removal, put standard regulator, put spare mask) in approx 10 seconds, give or take few more. Reversed operation takes a little more time because of time required to adjust the straps of ffm after donning it.
My vision is also that everything will break eventually, I'm an engineer. As you say, this is why I keep 2 tanks, 2 1st stages, and 2 2nd stages even on ffm. This is the reason I am not willing to use a gas switch block and rely only on one 2nd stage. But I really want to understand what possible scenario will result in mask failure (except regulators). At this moment, all I can think of is a hard impact with a rock or boat. But if that happens, my problem will be bigger and presence of another standard configuration (regular mask and two normal 2nd stages) won't solve it.
On the other hand, I just came from the pool, today is the first time when I tested this configuration. As expected, there were some differences between theory and practice. It was a successfull test, it performed more or less like I expected and for me this is a green light to go on further with this configuration.
Some observations about the test:
-it was performed in a 4 meter pool, no bcd, 2x4 liters steel pony sidemounted with 2 apeks ds4 1st stages and apeks atx40 2nd stage besides the built in 2nd stage. Also, shortie wet suit and 3kg weigth. A bit negative with empty lungs, a bit positive with full lungs.
-balancing the air flow was easier than expected. It was fairly easy to adjust cracking pressure on both regulators to a point where air is consumed simultaneously and in fairly equal quantities from both tanks.
-from the cracking pressure of the 2nd stages, I was able to completely close the mask built in regulator and breathe from apeks 2nd stage, but I was not able to completely close the apeks and breathe only from mask built in regulator. Mainly because apeks is tuned from factory to have quite low cracking pressure, to be easier to breathe. But I will adjust it a bit to be harder to open. On the other hand, mask regulator have a very wide range of adjustment, at one end it freeflows no matter what, at the other you almost cannot breathe without pressing purge button.
