One thing the Clays guides won't tell you (or any online resource) until it is too late, is that for the untrained and newbie, a pinball machine can be extremely deadly because it's obviously a 240 volt electrical item. That lesson may not be the first thing you read online but it needs to be.

If someone has told you, and u keep the coin door open, the high voltage mostly is disconnected "generally" but I have seen brand new people lifting the playfield with the coin door closed, screw driver in hand and totally unawares that they are seconds away from serious injury or death because they don't understand that 240 volts is not like 12 volt toys and they don't know what is or isn't safe under a playfield or in a backbox.

This is why the hands on courses (no pun intended - shock shock electrocute) are the answer for people who are not electronically or from a background dealing with electricity).

This makes these courses extremely relevant.
I saw an injury a fellow sustained from his first pin and the burns and scarring on his arm from an electrical mishap were pretty serious.
He just thought he would have a poke around and understandably he didn't know he was playing with something dangerous.
Even experienced people sometimes take shortcuts and forget coin doors and the basics.
That's where the AMD course is relevant cause it opens with safety first and the basics of all pinball power supply etc.
$595 to learn how not to get electrocuted sounds reasonable for people new to their own maintainence.