three questions:
are spys good?
and
what do they do exactly?
and
do u need alot of men to go with them to battle?

1.
spys can change a war completly, so yeah they can be good if you know how to use them, me and a mate killed 70 squads with just 40 squads because we used spys, we didn't lose much ether

2.
spys can do several things, when on your colony they can make spy protecton to help you if some one try to use a spy on you, when on op/colony of some one not in ur alliance they can make all vehicles, infantery and tanks hp 1 if you got enough energy and infiltration ticks.
and if you get the spy academy you can do lock down which make it imposible for people to send units out, and i thing imposible to relocate.

3.
to train 1 spy it take 1 worker, and spys make you able to fight bigger armyrs, but there are always limits

thnx 4 tht