Had a chance to check out 2 of the 3 flash modes in overcast daylight,

The slow flash, which is basically a slow fade between high and low beam, is rather visible in daylight but doesn't scream "I'm here". It works well in the dark without being obnoxious to the user and others like an normal flash.

The regular flash is a normal on-off flash rather than a "strobe". its very visible and attention getting.

I couldn't check out the "light horn", which is a burst strobe flash, by myself, but observing it in the dark while riding leads me to believe it must be very attention grabbing.

One minor disappointment is that unlike the Luxos U, the light must be on to flash the "light horn".