I had a choice with these LEDs (the brightest I could find) of (1) unfocused 90° FWHM, (2) 30° focused, or (3) 15° focused. I chose (2) as a reasonable compromise between (a) concentrating the light where I need to see it (down at the ground) and (b) spotting it somewhat off-axis as the rocket sways under the chute.Regarding the 30 degree spread making the lights harder to see.
Your eye is only going to capture a fraction of that 30 degrees, the rest is focused elsewhere, so it will appear more dim than if it were a narrower beam.
I work for an aerospace company, and I'm surrounded by pilots. My current project is doing flight tests with a Cessna 337, maybe I can have them take along a test strobe on our next flight test. Interesting idea. I do have a spare LED and MOSFET....