Davebuck-
The Spyderco Poliwog would be, in my opinion, too heavy to serve well as a keychain knife. In my belief, a keychain knife serves as a backup or supplement to the EDC that one carries in his or her pocket and is not the primary edged tool to carry. That being said, a medium-sized knife like the Poliwog would be in the definite upper (size) echelon of keychain knives. However, with its wide design, heavy stainless steel handles, comprably heavy ball lock, and other features, it would not favorably impress you as a keychain knife. However, it is a good design for pocket carry and some EDC use. Also, the CRKT Van Hoy SnapLok 2 is also a less-than-acceptable keychain knife in my personal opinion and was not designed for that purpose (or, as far as I can tell, for any real purpose to begin with).
In the department of true keychain knives, I highly recommend to you the new Spyderco Ladybug 3 (in fiberglass reinforced nylon---FRN---or stainless steel handles), the Spin, or the carbon fiber or FRN Cricket. These designs would serve much better in the capacity of a keychain carried knife than those choices you have listed. All of these designs would completely, to put it bluntly, "own" the CRKT design in utility and performance. These designs cut like much larger knives and have some of the highest quality in the production industry, especially for the price.
I hope I helped.
God bless you, America, our Allies, and our men and women overseas.
KATN,
Wade