These aren't using the Fisher refills. They're from the same company that makes the Sharpies. These claim to write under similar conditions and have a smoother line. The Fisher cartridges can smear a little after writing. The Uni-balls are dry within seconds. They developed a system to get similar performance at half the price. IIRC the Fisher refills are about $5 each.

Edit
I don't know about the top end of the heat range but they work at car in afternoon sun temperatures.