ssembo, that link is very interesting.
In my experience I prefer the 3 light method, if you have no synchronouscope.
By cross phasing two lamps you can switch with one light dark and two equally bright and close the switch.
The lamps have to be rated at twice the voltage and should be of clear glass.
When out of synch the lamps go on and off after each other, when the generators are nearly at the same speed the lamps slowly go, off, dim, bright, dim and off.
Major damage will occur when generators are out of synch. and the parrallel switch is closed.