My biggest worry would be the joint at the bottom (the four bolts visible in the video) giving way because the tension is across the top of the wooden beams. That won't end well because suddenly the winch becomes the projectile.

Also, there's not a huge angle from "where the ball is supposed to go when it fires" to "where he's crouching adding energy to the system".

Yes, that seemed a disaster ready to happen, especially as it was already loaded. He must be very confident of his release system.

I would definitely not watch Colin Furze

I can't stand that guy due to the way it is all presented, it's like watching 'Blippy for adults'.

You obviously haven’t seen the Blippy Harlem shake meme.