As has been said many, many times in this and other threads the service that Jerry at Stillwater provides is indeed second to none.
(I own 2-Thrifty Kilts, 1-Economy Kilt, 2-Standards and 1-Heavyweight)

The Frugal Corner is still learning the ropes. They've moved and had a change in ownership. Service can be spotty, but they are trying real hard (at least in my experience).
(I own of their 3-16 oz. kilts)

They may or may not have the same supplier, however the fabric is not the same! The fabric on FC's 16 oz. feels heavier and is a bit stiffer, has nice swish. SWK's fabric is softer and seems to pill more easily.

Both are great values for the money.

Hope this helps,

Marshal Moroni