As mentioned earlier, the tail yank works really quickly with mice. Rats are another matter, though. Too much musculature in the neck, I suppose. I've met a lot of other breeders who switched to CO2 as soon as they got into rat-eaters. With rats, I learned that a hemostat placed 1/4 to 1/3rd way down the neck and a quick clamp breaks the neck instantly, but that said, I'd never go back from CO2 (or buying f/t) now.
As for keeping a feeder animal, I have kept two rats as pets destined for feeders myself. One when I was a teen that I offered live to a big black rat that wasn't in the mood to eat. He essentially "fought" with his meal, and was losing so I removed it after several bites. The rat suffered some sort of damage and couldn't fully use its hind legs, though wasn't fully paralyzed. I named him Ironsides and he would ride in my remote controlled car! He never recovered but to memory lived quite some time and made many trips up and down my driveway over the course of his life instead of being digested.
The second one was just a couple of years ago. A local breeder here had some hairless rats and wanted me to sell or feed off the males he produced. I had all plans of putting them down, but one was just too interesting! I put a running wheel in the cage and he went right up to it, stood on his hind legs and spun it with his hand. Best part was, he would spin it as hard as he could when his brother would get in it! I sold his brother, and his behavior got even more interesting. He began to run in the wheel, but only if he thought no one was looking. Every single time, he would run so fast the wheel would flip him *until* he saw a person... then he'd get out and spin it with his hand! I got such a kick out of him I kept him around until a kid in the store wanted him for a pet. FWIW, I've never felt okay feeding "tumored" rodents to my snakes, even though I know consuming cancerous cells can't cause cancer.
*some details in this post may be inaccurate, due to the fact I'm recalling events that occurred when I was about 14.