I reviewed a set of LED lamp bulb replacements that were guaranteed to have twice the lumen output of incandescent's they replace. I believe I would pick them any day of the week over alternating incandescent lamps for visibility. Same for adding a nice LED "third brake light" between the two lamps. The Mexican PFP (Federal Highway Patrol) has LED light bars when switched to "Hi" can be easily seen for 5 kilometers. A rhythmic strobe pulsing effect. Alternating flashing incandescent lamps would "look cute" but in my opinion do zero to aid safety or security.
You are chopping total lumen output in-half and lumens are what keeps the vehicle behind from eating your rear bumper.