These "gimmick" shotgun shells are just that: Useless gimmicks sold to people who just want something "cool".
Flechettes were tried in Vietnam, and proved to be a failure.
The problem is, they're needle-like aluminum or sometimes steel darts, that have almost no mass.
Although they carry pretty far, they don't penetrate very well.
Half of the Flechettes are packed into the case backward to allow more to fit in.
Many of these fail to stabilize and hit sideways, so they don't penetrate at all.
The big problem that turned up in Vietnam was, even people with fatal wounds often didn't know they were hit until they eventually collapsed from internal blood loss.
The low mass needles simply have no striking power.
Yes they are often fatal.......eventually.
"Eventually" is not something you want in your face some dark night in your living room.
The "Dragon's Breath shells are not only useless, they're ludicrous.
Precisely what use do they have, other than to impress the boys at the range?
They have no self defense use, and think about trying to explain to a court all about how you shot someone with one.
Again, all these "trick pony" shells like Flechettes, flame shells, rubber balls, "Bolo" rounds, and other junk are useless in the real world, expensive, and sometimes damage your gun barrel.
NOTHING says "Stop that, leave us alone" like a load of standard buckshot.
Also should you actually have to shoot someone, you won't have an entire courtroom looking at you like you're got three heads, or like you're dressed like Adolph Hitler.