I have never tried the Comfort Zone, in answer to your question, although I've seriously wanted to try it.
I had sort of a different experience with my two cats! I guess they were "meant" for each other...
I read all that stuff about how to introduce your new kitten/cat to an existing cat and was SO nervous about bringing Jasmine home b/c she was barely 6 weeks old and oh so tiny. Leo has always been a gentle cat and very loving but I was still paranoid to death that he would hurt her. I had planned to do it RIGHT BY THE BOOK.
The minute I brought her home, I let him sniff her in her carrier and of course his tail fluffed out but no hisses or growls. Then I took her to her "room" for the night, shut the door, and let her out. Leo just sat outside the door waiting for a chance to come in and check her out. I finally said what the heck, wrapped her in a towel and holding her very closely to me, let him in.
He walked right over to her, sniffed her, then licked her very gently on the top of the head several times.
Never one time did he hiss or growl or even act aggressive. Of course, he was cautious around her but my biggest problem with Leo is he thought she was a new toy and kept trying to grab her and roll around on the floor! I kept her closed in a room when I wasn't home to supervise, but within less than 2 weeks, Leo had accepted her as one of the family and I could trust him alone with her. All the books say 6-8 weeks, but it really depends on the cat.
Leo had always slept with me and after bringing Jasmine home, it was a good 6 months before he slept with me at night again! I think he had thought I replaced him but I made sure to give him lots of love and attention and he soon learned he had not lost his "status". Now he's right back on top of my feet where he used to be.
Plus, he and Jasmine are great playmates.