If you're really concerned about it, you can purchase a separate temperature controller. Aquarium heaters are notorious for malfunctioning, so people in the fishkeeping community recommend using something like this: Ink Bird Temperature Controller

I don't have one of these for my brine shrimp, but do have them on my regular aquariums. They work well, but the manufacturer directions are terrible, so if you get one I'd recommend watching a YouTube tutorial on it before setting it up.