I've been neck carrying a La Griffe of some sort since 2004. The reason: Top line defense. I was once assaulted at a "friendly" get together by a drunken giant brute of a man who caught me from behind and put me in a bear hug so tight that I could feel my consciousness slipping. I instinctively reached for my P'Kal but couldn't reach it due to the way he had my arms bound up. I had enough elbow movement freedom to reach under my shirt for my La Griffe and proceeded to give him about 1.5" deep, 4" long gash in his arm, which made him immediately let go. If I didn't have my La Griffe on me, I may not be here telling this story. I carry top line (neck knife), mid (pocket and belt buckle knives), and low (repurposed neck knives laced into my shoes/boots). That way, no matter what compromising position I may be put in, I have access to a blade. If weight and comfort are a concern, go non-metallic or get a Warren Thomas. I traded my Emerson La Griffe for a CF/Ti WT recurve tanto La Griffe and it's so light and unobtrusive that I fall asleep with it on just about every other night. Find the right neck knife style for you - one that you can handle safely and with confidence, and one that won't swing around your neck like a Flava Flav alarm clock. People are shaped differently so a neck knife that works for one person may not work for another.
If you've tried a necker and don't like it, try a different one... and give it a chance. It's like getting a tattoo or something - you will definitely notice it at first, but after awhile you'll forget that it's there.