That's a good point, it doesn't explicitly say how to use them like how the Mods and Weapons descriptions do.
Text says: "[Specials] Are abilities or devices that can be activated by generating 1 Heat. They last for 1 Round and can be used Once per Game, unless otherwise stated."
Reading in to that, my guess is that you can use any number of them on your turn, each once per game. The downside being if you use too many in one go, you'll overheat your mek and kablamo.
But yea, I think the language in that description could be a bit clearer on how/when they can be used.
If they are meant to be used as above, maybe a description like:
"[Specials] Are abilities or devices that can be activated (on individual Meks once per turn/once per Mek, per turn) by generating 1 Heat (for that Mek). They last for 1 Round (unless otherwise stated), and can be used Once per Game, unless otherwise stated."