I've carried Fox, Mace, Spitfire, the Kimber Pepperblaster and others.
As I posted in this thread with pictures, the Fox keychain design is the same generic plastic case that Sabr and DPS use.
Personally I think it is poorly designed. The 'safety' on both my Fox keychain units is quite loose and can easily become caught in keys/pocket, risking an accidental blast of 5.3 to the groin. The Fox unit itself is also very big and looks ridiculous in dress trousers or anything fitted.
I ended up switching to the Spitfire, which you can see in the pictures in the thread above is more streamlined and requires a very specific action to fire.