I have made a few kit purchases directly from Sig's web site recently. This was in response to Tower discontinuing Sig's product line. I have to say it was a very positive experience. My merchandise always arrives within three business days from the receipt of my order and the boxes—both the shipping container and its contents—have always arrived in excellent condition. Shipping seems to $8.99 regardless of what you're ordering. That may hurt if you're ordering small accessories. I can't speak for shipping costs when ordering outside the United States.
If you're looking for a Sig kit and can't find it at your favorite store or web site don't hesitate to order directly from Sig. I've really been happy with their service.