I have been trying a lot of coffee mugs in my carreer so this one also got me interested. But I have to agree that porcelain seems to be the wrong choice.
I haven’t tried a Mo Mug, but I think porcelain was the wrong choice. The seller is correct that plastic alters the taste of hot drinks (as does the stainless steel in most travel mugs), but porcelain needs to be so thick that it acts as a giant heatsink, causing the tea or coffee to lose heat far too quickly.
The borosilicate glass Marco is referring to is at the moment my number one choice if I want to enjoy coffee. I especially like the double walled glasses.
If you want to make a reusable coffee mug from a breakable but flavor-inert material, borosilicate glass is a far better choice: it can be much thinner, and a double-walled design will insulate far better with much less material.
My number two choice, the one I use most of the time for my coffee is a titanium double walled mug, just because I break one glass every month or so. In my opinion titanium is a far better choice than stainless steel, firstly because it doesn’t alter the taste as stainless steel does, secondly because of the insulation and thirdly because of the weight and the endurance. I carry it around all the time, for almost 4 years now.