How works tier 1,2,3,4 units offered?

[Mr anus]

I click on this upgrade and nothing happened. What is this upgrade do?

[Valthejean]

It means when you get rewarded with those units such as when you beat a wave, it increases the number of units you get by that amount. Do note that you only get rewards from the highest tier you've unlocked. So buying this upgrade for tier 1, for example, will no longer be in effect once you unlock tier 2.

[fluxtorrent]

yeah its a trap upgrade up until tier 5, don't waste your precious coin on it

[Nightfish]

Whenever you select a unit after a battle or from the shop, the amount you get is increased by as much as it says. It's fine to buy this if you plan on taking units since each time you get this, future upgrades seem to be cheaper. If you wait until tier 5 to get this, it will be really expensive and you've missed out on a lot of "free" units in lower tiers.

[Mr anus]

TY all, guys!