I have used pen gun flares, during SAR ops, and they did the job. We didn't have 12 gauges available, so no experience. But if your kit includes a 12 gauge, flare rounds would make sense.

But any flare has a drawback. It is a one use item, and it probably won't mark your location as precisely as a stationary strobe right at your scene.

Some years ago, I and a SAR colleague encountered a serious accident scene while on a recreational climb and boy, did we have to improvise! We marked the hoist location with a large impromptu bonfire (quickly doused once the helo had us spotted).

Improvisation is often necessary. You simply can't carry everything that might be useful. Stuff must be versatile....