I think it depends on both the kilt and the sporran. I'd never consider wearing, say, a fur sporran with a UK, but a plain leather sporran would work fine. I almost always wear a sporran with my TFCK kilts, but they're so close in appearance to a traditional kilt that most people don't notice the difference anyway. Still, my sporrans tend to be on the plain side - my fanciest sporran is Freelander