I carried and qualified with a P3AT as a BUG for a few years. One finger on the grip is less than ideal, but hey, it's a deep cover, always there, insurance policy! The Walther is certainly larger and somewhat easier to shoot than the KT. If you carry on the vest, the larger gun might not be such a problem. (Still a .380) There are 9mm pistols out there that are no larger than the Walther, and thinner/lighter to boot. I went to the KT PF9. Currently Taurus, Kahr, Sig, and likely others I'm missing, make pistols in the same size and power class. If you stick with the .380, I'd take the time to master the KT.
Savage