The 5.7 is controversial in gun circles as an extension of the epic/ongoing "Momentum v. Energy Wars" everyone seems to take sides on. The 5.7 is pretty much the fastest, littlest bullet out there (that is still pistol-able), and that bugs the hell out of folks who believe damage comes from mass (not speed). If there was a super heavy, super slow round that would still fit in a pistol (.45 long colt cowboy load?) similar bashing would probably come from the 5.7 and magnum guys.
Myself, I'm a hot-rodder. I own a Five-seven, a .357 Magnum, and a CZ-52. Those are all well on the side of Energy as opposed to momentum, as far as ballistics (yes, .357 is more flexible in this regard.) I personally find sharper, shorter recoil more controllable in handguns. I feel like the bulk of my mass is pushed around less after each shot (momentum).
However, my taste is opposite in rifles, I prefer slower, heavy bullets. Unlike pistol shooting, your elbows don't really absorb much energy before the impulse meets your (relatively) fixed shoulder, so your tissue must dissipate the momentum transfer directly (ouch). Though a slow, heavy round hurts, the impact is softened by duration, your "fixed" shoulder is better suited to soaking up momentum than a skinny arm (well, mine anyway). My next rifles will be 7.62x39 and 45-70. I currently have. 308s, but I have come to the conclusion their high-speed flat trajectories are unnecessary for the distances I shoot.
Ultimately, to claim energy or momentum to be paramount is silly, since the same two terms (mass and velocity) show up in the equations for both, they are two sides of the same coin. An infinitely heavy bullet cannot move, and can do no harm. A completely weightless bullet will come to rest instantly without penetrating, and can do no harm. In my completely unqualified opinion, I think we crossed a threshold with smokeless powder, where
any centerfire round has the energy
and momentum to be effective, and the argument is therefore moot. Let's instead debate whether a flared-end on your Blunderbuss improves your patterns!
It's a personal preference thing, and you won't know where you stand until you shoot a five-seven, and satisfy your interest in its capabilities. Personally, I have found my arms are better at quickly dissipating energy without losing my sights, than my overall stance is at recovering from momentum transfer. I chose rounds that fit me best
(but boy are they LOUD!
)
TCB
PS: "He is joking. THR does not have religion or politics forum." Coulda fooled me...
PPS: Forgot to answer the OP's question: Both. It's a bullet, it will maim or kill depending on what it hits.
The real truth of the 5.7x28 round is satisfying to neither the fanboys nor the haters. Reality rarely is.