Bob S.,
The real advantage of the Mustang and Pony is the locked breech design. This cuts the felt recoil in these small guns considerably. Most .380s are blowback systems and tend to have a sharp, nasty recoil. I have seen and shot the pony, but didn't care for the trigger action on them. I suppose a good gunsmith could fix it though. I would recommend Scott/McDougal for any work on one. Sorry, but I don't have any experience with the Gaurdian or Seecamp guns.
Truth is I'm not much for pocket guns. I was looking for a small auto for hot weather t-shirt and shorts carry. Since my normal carry gun is a .45 commander, the Mustang was the natural choice for me. Still I don't carry it in a pocket but carry IWB under a t-shirt.
I really can't give any advice for pocket carry except for a J-frame S&W .38. I suggest you start a new thread on reccomending small autos for pocket carry. I'm sure you'll get all the info you can use.
Frankly, the Mustang is an excellent little gun. They were designed to carry cocked and locked and are perfectly safe that way. If you can get over your doubts, I'm sure you'll be happy with it.
BTW: If you decide to keep the Mustang, put in the Scott/McDougal trigger and stainless guide rod. These two mods will increase reliability and are definately worth the money.