I've just recently gotten into neck knives - now I'm a big fan. I like Livesay knives, so I bought a cord wrapped LP, and a plain handled WOO. I just got back from 10 days in the mountains (near Pike's Peak). I wore one of the neck knives constantly. The LP has a 3" blade, the WOO is about 3 1/4. Both are 1/8" 1095 steel. I think the overall length is about 7 1/2". I don't know the exact weight, but neither were uncomfortable. The LP has a better utility geometry, so I usually wore it. No matter what kind of shirt I wore, the only thing noticeable is the knot in the cord at the back of your neck. I can't tell you the number of times I've gone into REI, and had someone ask me what kind of pocket knife I carry (they notice the clip). I've never been asked about the neck knives.
I like folders, but I prefer the extra utility and security of a fixed blade. To me, accessing a neck knife is just as easy, even one handed with a shirt tucked in, as any folder. The only advantadge a folder has is they are easier to put away one handed (for me, not a big issue). The neck knife has many advantages - it'll never fold over on your fingers, no matter what you do, it's more concealable (no pocket clip), it's less threatening to sheeple (are you getting a quarter from your pocket, or your folder?), it's thinner and lighter than a comparably sized folder, easier to access in some situations (sitting in car with seat belt, no pockets, etc.) ,etc. etc.
Just my opinions, I still like and carry folders, but I now prefer neck knives...