Having owned both, I went with the Shield just because the quality was nicer. The shield feels better in the hand, more ergonomic, though the Kahr isnt that far off. Both are still thin and very easy to conceal. My biggest complaint with the Kahr, was field stripping it. Nowhere near as easy as the shield to field strip. Also the Kahr doenst have metal guide rods and after using it for a bit started seeing some plastic shavings. I heard this is normal to happen for the break in on the Kahr's, but I couldnt get past the plastic guide rails.
Shield feels right and feels good, no regrets buying it.
Hope this helps.

Note: I love Kahr triggers, and will probably own a Kahr, but it will be the steel frame versions, K9, MK9.