I've been carrying my keys on an ASP Key Defender for over 10 years. Originally, I got it to provide redundant backup for a pocket OC canister and an ASP baton - over the years, I have found that it offers me a synergistic combination of features and options that no other pocket stick or OC system does.
Normally, I like to carry the KD inside my waistband just forward of my IWB pistol holster, with my keys hanging outside. This allows me to quickly and easily pull the whole unit free when walking up to my car or front door, or if I perceive a potential threat. If I glide my fingers between the keys and my belt, and lift by the key-ring, the KD comes out into my palm ready for immediate use. Alternatively, I can leave the KD in my waistband, and release my keys alone with the quick-detach key-ring they are on. If the keys jingle too loudly for comfort, they can be tucked into my side-pocket and silenced.
When my car key is in the ignition, the KD hangs next to the steering column and can be released via the QD key-ring if a panhandler in the parking lot or on a median looks like he might get aggressive.
While walking with my keys, I like to hold the KD in a ready grasp and let my keys dangle from the top of my fist - this lets me flail with the keys, or do a
punyo pommel-strike or hook/trap with the spray-nozzle-end. This hold also allows me to surreptitiously activate the OC and lay a smoke-screen of pepper-spray behind me if I think someone nefarious is following me too closely.
Of course, the keys can be carried in my palm for silence if desired.
The OC formula is suitably unpleasant and nasty, the knurled aluminum body works pretty well as a Kubotan, and the safety-catch is effective, ergonomic and reliable. I cannot imagine carrying my keys any other way than on my KD, and it goes with me any and every time I leave my house.
How's that for an endorsement?