Boosters

Amplifier's damage bonus stacks linearly, i.e.:

1 Amplifier in a room results in a +65% damage bonus

2 Amplifiers in a room results in a +130% damage bonus

If you shove an Amplifier, its throughput is massively increased (to almost double, playing as Sweeper with perhaps one or two boosts to the Wit stat, around a value of 20-25). 

However, this bonus is not applied to Heroes unless they leave and re-enter the room while the Amplifier is boosted. 

However II, the buff will last indefinitely on a Hero, until leaving the Amplifier's room.

I think the last two points are an oversight that needs to be addressed.

Presumably (untested) this is the same for the Shield.

Hinderers

The effects of Jellifier and Sapper units are persistent for a few seconds after the affected entity leaves the area of influence.

Levelling up Hinderers makes their radius larger.