It seems like the question is, are you trying to stop the opportunist or the determined thief?
This bag will definitely stop the opportunist, and may be overkill for that scenario. For example, even an $80 Tom Bihn DayLight Backpack will stop slash and grab opportunism, is almost totally waterproof (not submersible) and you can add a simple chain lock that'll secure it.
This bag isn't going to stop a determined, equipped thief and, by having such a bag, you're advertising that you have valuables in it so one could argue it's actually going to attract attention you don't want.
That leaves the scenario where you want maximum protection against opportunism and the bag is out of sight like in a car or hotel room, but one has to wonder if you should even be in that scenario in the first place ...
Seems like a great product, but I"m sure what the use-case for me would be.