Would it really be broken if the cluster mines were only tied to cooldown? It's an ability i quite like but it punishes squad preservation because of the 3 mines per squad limit. If you really want to use the investment of unlocking them in armory you are better of with getting new scout squads than reinforcing them ( which is even further pushed by the fact that 1 scout model left is as good at throwing a stun grenade as 5 in squad ).
Maybe increase the cooldown if necesarry.
I might be in the wrong here, so i want to hear opinions. I dislike abilities with finite resources.
I'd also like them to explode maybe 0.3-0.5 seconds after being triggered, plenty of times enemy squad runs into a mine and it only hits one model due to spacing and the explosion having not that big of a radius. It would help with making the explosion happen closer to the middle of the squad.