Only if done correctly. Could get more inhumane, painful, and cruel if someone messed up a cervical dislocation for example. One can end up with a live, but paralyzed feeder. And CO2 isn't painless. It burns the eyes and nose for starters. I've euthanized hundreds of lab rodents and I can tell you, while it is the most humane out of all the official euthanasia methods, it's not painless or comfortless.
I don't do pre kill for my snakes. They're good at what they do. They are efficient and quick. Just as fast or faster than the CO2 chamber. Especially since I usually just feed smalls. The big girls take them down fast. In seconds really. By taking down, I mean the feeder is dead. I can't really think that is inhumane when the feeder is only in a coil for a few moments. When coiled, endorphins kick in and dull the feeder's pain receptors down.
I do pre-kill feeders sometimes for my ferrets. They're darn good at killing prey, but they're not as efficient if the prey is too large. Plus, larger the feeder, the more it tries to resist, fight or defend itself. The feeder also has a higher chance at hurting itself and suffering a long agonizing death if its too large. A ferret cannot restrain a big rat like a snake coil does. So to keep things safe and relatively painless, I may PK occasionally. But only because the pros and benefits of PK outweigh feeding them live if the feeder is too large. With smaller prey and for the snakes, not so much personally.
Sent from my DROID RAZR using Tapatalk 2