This site states this specific detail directly on both its 3- and 6-bottle pricing cards: free US shipping.
Worth noting this benefit isn't reserved only for the 6-bottle "Best Value" tier — the 3-bottle "Most Popular" tier carries the same free-shipping benefit, worth factoring into your tier comparison.
Since free shipping applies to both larger tiers, the per-bottle price difference between them becomes the main cost factor to weigh, worth checking against this site's own cost-per-day breakdown.
Backed by a 60-day money-back guarantee.
See The Current BreathiZen Offer