When it comes to pistol calibers, raw kinetic energy isn’t really a factor, they’re just too weak to actually induce any sort of hydro-static shock that could cause a permanent rupturing of nearby tissues, you need much higher velocities or energy to do that that, which only rifle rounds or shotgun slugs can reliably induce.

For pistols, the only mechanism of action they can rely on is the mechanical size of the bullet itself, as the bigger the bullet, the larger the hole, and thus the faster the blood loss. Hollow points are the best method to cause bigger holes.

Ballistic gel is a somewhat deceptive testing media, as it can show a big permanent wound cavity beyond the size of the bullet itself, which isn’t actually how it would perform real tissue, which is able to stretch much more than ballistic gel. What really matters for pistol rounds are being able to expand as much as possible while also maintaining adequate penetration (12" in gel), so that you can reliably penetrate bone and muscle to reach critical organs from any angle. You also want to ensure that the specific hollow point chosen isn’t prone to being plugged by heavy clothing if you live in colder environments.

LuckyGunner provides the best comparison of bullets that I’ve personally seen for every pistol caliber, allowing you to avoid bullets that don’t adequately penetrate, expand, or over-penetrate.

All pistol defensive pistol calibers break bone when struck, the xtreme penetrators will simply penetrate further and through more bone than a hollow point. This makes it act similarly to a hardcast (ultra hard lead that doesn’t deform) flatnose bullet, which are also usually only recommended for bear protection.

Over-penetration is an extremely negative trait in personal defense against humans, as it means that the bullet will pass through the target into anything behind them, including innocent who you do not intent to hurt. In self defense rounds you want the bullet to stop inside the first target to avoid endangering anything behind them.

But how do you assess value?

Xtreme Defenders are a good value for bear protection, but are extremely poor value for self-defense, as they are more expensive than a good hollow point while providing less effective wounding characteristics and increased danger to bystanders.