I bought the Stein Double AC as an upgrade to the cheaper plastic Thomann/Focalink Plastic AC (which also is a great instrument, by the way).
The first thought upon unboxing was that it was a beautiful and precious piece of craftsmanship. It has a good, solid weight and a nice straw fired (and therefore unique) glazed texture. There is a hole so that it can be worn around your neck, but a neck cord is not included. It might be a good idea to invest in one however as clay ocarinas are a lot more sensitive to drop accidents than a plastic ocarina.
There is a slight burnt smell to it, which I happen to like. If you are sensitive to smells, you might not like it but the smell will decrease somewhat over time.
It is designed to be comfortable to hold, and the glazed texture makes it easy to slide the fingers across subholes or across different chamber holes.
It uses a rising breath pressure, meaning that more air is needed as you go up the scale. Acute bending (looking down) while playing the higher notes is not necessary at all.
Unlike plastic ocarinas, this ocarina does not have condensation issues meaning that the clay will do a good job at absorbing spit inside the mouth piece, so that the ocarina will still play well even if it hasn't been cleaned recently.
An argument for getting this ocarina for me was the second chamber. In hindsight, it might have been more of a psychological thing than an actual problem, since I most frequently only use one chamber. It might feel nice knowing that you can go higher if you want to, but for me personally the higher notes sound a bit squeaky and I would rather have a two chamber range that is transposed one octave down.
I like the instrument and would recommend it to anyone looking to buy an ocarina with a high degree of craftsmanship. If a single chambered version, otherwise identical, was available at a lower price I might have opted for that if I was to buy an ocarina again, but it still feels like it was worth the cost.