We use the Stellar 2.0 for biathlon races, and they work very well. They aren't meant for -20 C, but neither is biathlon racing. We haven't tested all conditions, but these gloves are a good option when the temp is below -9 C or so and you're moving. The index finger fits inside the trigger guard without issue.
My hands measured at the upper end of the Medium scale but within it. The fit is snug, and I would order a large next time. My wife has large hands that hit the middle of the men's Medium range, and these gloves fit her perfectly.
Would recommend!