Both are a single upfront payment covering the whole term plus a 2-month wrap-up window. Full-Mission gives you your page, your own custom domain (you set up the DNS, we guide you), and photos & attachments. Pro adds the premium bundle (a managed custom domain we register and run for you, Photo Pro with full-res + 5 GB, and the PDF Letter Book at homecoming) for an honest $20–$45 less than buying those pieces separately.
Mission length is known at signup for almost everyone (Elder = 24 months, Sister = 18 months), so the upfront ladder is the natural fit. Senior couples pick the 6 / 12 / 18 month option that matches their call.