5 ball option is there so if they like it use it!
Who likes change and your taking 2 balls away. Wtf!!
But ..
Scoring and rules are sometimes changed so if you want to get them used to three ball have them try to figure out the differences.
Ie) pops scoring more
From my memory most all EM were 5 ball.
But as solid state games came out and well games with longer play time and the boom of arcades. If your playing your not putting the next quarter in right. So blame the change on the operators but it has been pretty standard for 30+ years.
Get them used to the real world is what I would do.
And remember it is all your fault for ever having it set to 5 ball to begin with.