Energizing a vacuum-tube flip-flop module from a 1948 IBM system

Author here. I've powered up another tube module from the IBM 604, so let me know if you have questions...

What was the failure rate of those vacuum tubes, that they had to be so quick & easy to replace?

I'm also curious, if the cathode was grounded to the machine frame, how dangerous was it to do work on those machines?

integrated circuits were only invented a couple years before the Apollo moon missions started in 1961

imagine an alternate timeline where that didn't happen, could moon landing have even happened with vacuum-tubes? highly unlikely