Pretty easy. Majority of parts were also used by their flipper games. Very robust and generally not destroyed. Generally being the key word.
No bingos came from the factory (except one) of the 139 games produced with a coin payoff option. Even for that one it was totally optional.
Nope! Again, very robust.
They are a joy to work on and a thinking person's game. The action is all the drama in build up of features and the agony of missing a number that you need. Another ball is right around the corner to definitely 100% make it into the hole you need
... this time. There are tons of features that allow you to physically move the numbers on the card, change the layout, or return some or all of the balls to be replayed. Endless depth, endless challenge.
Working on EMs is quite fun and pretty easy. It's a matter of logical thinking and testing assumptions based on reading of the schematic (and manual if it's a bingo or very late flipper game).
Above all types of games I work on, I vastly prefer EMs. I help people all over the world work on their games (as do many that have posted in this thread). EM schematics are great!
Games from the 30s and 40s are challenging if you don't have EM repair experience (since there are usually no schematics), but after you've worked on a couple of games and understand the general routines for startup and gameplay, you'll be able to troubleshoot them as well.