Well at 70 yards 00 buckshot will still go straight through a 2x4 or 2x6 and flechettes would barely leave a mark or barely stick in. I'm sticking with the buckshot. The inconsistencies alone make flechettes dead to me.
only way I'd use flechettes would be in a "punt gun" type application - basically an untargeted broadside where volume counts against a mixed mob - a flechette or two would be a mind changer to some - mixing in some "rat shot" (#10 - #11 birdshot) wouldn't hurt ....
So a house invading door crasher would not make a good target? My thinking is that it is a short range discourager at the very best. Over say 10 yards, go with something a bit more damaging and reliable. "Mixed mobs" will be better handled with targeted rounds, buckshot is one, 556 is another. IMHO, anyway. I've another opinion regarding untargeted firearm discharges, but that will keep for now.