Over the years I've tested/regularly worn each of the following as an EDC light on a beaded steel chain necklace:
-- Arc-P (AAA)
-- Peak Matterhorn HA 3 LED (AAA)
-- Fenix EO (AAA)
-- Fenix E1 (AAA)
-- Infinity Ultra-G (AA)
-- Inova X1 (AA)
-- Peak Kilimanjaro Brass 5 LED (AA)
-- Peak McKinley HA 7 LED (CR123)
-- Fenix P1 (CR123)
-- Fenix P1D-CE-Q5 (CR123)
All these fine lights have their plusses. However, the Arc is, by far, the best overall fit for my needs. It's not the brightest, but it IS...
1. The thinnest/shortest/lightest (tied w/EO and E1): hence, comfortable and unobtrusive. An Energizer L92 lithium battery makes it noticeably lighter.
2. The most reliable (though others may equal it... under perfect conditions).
3. The best "hanging." On a neck lanyard or chain, the little Fenixen hang crooked. The Arc hangs straight.
4. The easiest to turn on/off with wet/cold/old fingers (superior knurling + non-fiddly/fussy ergonomics). This point is especially critical when you need a little light FAST... and when your main light(s) are buried in some pocket.
(Being a street-wise Flashaholic, you DO carry at least 2 lights at all times, dontcha?)
We had a good thread here 2 years ago about which TYPE of necklace or lanyard was best. If the Search key is working, I urge you to check it out. As I recall, most concluded that the regular old beaded steel chain was the best variant of this carry method. It's already been field-tested by the military for many decades (dog-tag I.D. carry). It's "combat durable," low-cost (about $3 US @ any hardware store) and its break-away-ness makes it the safest by far. [If a mugger ever tries to strangle ya, it'll snap just about the time you're able to (a) wave your Please Don't Hurt Me "Peace" medallion at him while begging on bent knee for divine intervention by Sarah Brady or the Tooth Fairy, OR (b) plug him with your .38 snub-nose -- all subject to your ideology-based grasp on reality, of course.]
Sometimes I carry my Arc-P necklace under my shirt. However, I've taken to carrying it "out" after sundown... just so it's always Right There... even in dimly-lit restaurants where the menu's stylishly illegible. No need to be self-conscious or defensive about this, or bow in wimpy subordination to ditz-brained wives/gf's who think all tools/flashlights/guns/knives are Eeeuwww!Yucky!Dorky! Besides, before long, you'll have too many good How-My-Handy-Light-Saved-The-Day stories to tell all those snot-nosed, Un-Situationally-Aware sheeple and assorted Big-Brother-dependent, metrosexual fashion critics (all illumination-illiterate Nanny-Twit Victims-Of Unplanned-Surprises-In-Waiting).
Arc-P + beaded steel chain. It works.