Guerrilla warfare an already very powerful strat already has marines for 80 cost, this skill takes it to 70. meaning if you guy 7 you get 1 free. Amazing upgrade for GW, most likely OP.
Master of stealth and strat that imho is a bit too cost intensive at the moment needs a little love, you have to pay 140 for marines, and this upgrade takes it to 130.
if you changed it to 10% reduction, it would help MoS more and help GW less.
new Cost with 10% reduction applied.
GW 72 per marine (hardly any difference but still less good nonetheless)
MoS 126 per unit , sure it doesn't seem like much but it would help. right now at only -10 i Don't think getting this upgrade is worth it from a MoS standpoint, but at a cost difference of 126 vs 140 I think I would be more likely to pick it up.
It's better to see it this way
That's 1 free unit every 10 you buy instead of every 13 with MoS.