The repair choices of prepaid and refundable postal packs are on the repairs category page, but you do have to scroll past a blank section.
If you pay in advance for the fixed price service you do not need to buy the refundable pack as well.
Getting a bit behind again, so 4-6 weeks is stretching out in most cases, especially as the temperature fluctuations always seem to lengthen the timing and testing periods post servicing.
With watches that were designed with built in temperature compensation that wouldn't theoretically be necessary, but Smiths aren't adjusted to temperature in most cases.