I have both. As said before, Swift is the better bike and Brompton is the better folder. I don't find biking on my Swift much different than biking on my normal bikes. Having said that, I don't find commuting with the Swift using trains etc much more comfortable than my normal bikes. It really does not fold very compact.

Snow or sand will always be bad on small wheels but being stiffer I think helps giving more confidence to the Swift compared to the Brompton.

If you will be duplicating, maybe but then rather your steamroller. The brompton is a different beast all together.

For rack I just put a Dahon rear rack on mine and I have used it with medium sized panniers with no problems.