i skipped to the 'good' bit of that video ..... its a "suck-it-and-see" method. Try all the numbers 1 at a time and try twisting the open knob. If the catch goes a tiny bit further on one number (and it looks like the slide move 1/5 of a mm further on a correct number) then thats one in the bag and you go on .... Could be worth a try (guy in video did it in 11 mins....) . Would be good to get the spare key out if it was in there. Wouldnt like to throw that away.
I like the angle grinder option myself ....
OR ...... drill 4 holes through the front to line up with the screws and unscrew without opening?