I actually ordered one of their test postcards yesterday, so I'll update you when/if it arrives.

Interesting that they don't require a postal address for each recipient (they say they'll take care of that part) – I wonder if they use their tight integration with Shopify etc. to match up email addresses with physical addresses somehow (but that seems like it would open up all kinds of privacy issues)?

Thanks! Some of the postcards go to people without email addresses: any clues how to set up data imports for this contingency? I was thinking of just appending a +refno to my username on gmail to keep up to uniqueness aspect (I couldn't see a requirement for emails to be unique but I can see it being a probable requirement.

The test campaign I did took over a month which is pretty terrible. The test card they offer came at the same time. YMMV.