yes, they do stack 🙂 But it’s not indicated in GUI in any way.
Laser shoots for 0.1s and charges for 0.9s. Each surrounding Booster increases Laser’s shooting time by 0.1s and decreases charging by 0.1s. In other words, you may boost a Laser with 8 Boosters to achieve 0.9s shooting and 0.1s charging.
I will mention in game description that they stack