I did a quick sublimation experiment yesterday. Results weren't impressive ...
I used a Listawood mug (that hadn't been pad printed on the base) and attached the transfer, with a 2mm thick circle of silicone over it to level any bumps, and a £2 coin and heat tape to add some pressure. The green silicone wrap was just to add some extra pressure to the ends of the tape. The mug was placed into my halogen oven at a temperature of 180° C, rising to 200° during cooking.

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In the next picture, the top mug was cooked for 9 minutes and appeared to be very feint.
The bottom mug was cooked for 15 minutes and, although slightly darker, much of the print was virtually missing.

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My conclusion is that, although more pressure may have improved things a bit, the coating on the bottom of these mugs isn't good enough to take a sublimation print. I don't have any other brands available to experiment further.
I might add that the base of the bottom mug, although looking smooth, did in fact have a depression when I ran my finger over the print, which is probably why it printed unevenly.
I have my doubts whether a press would achieve any better results as the advantage of using an oven is that everything is heated up to the same temperature. I think a press would struggle to heat the transfer enough if the entire base wasn't heated at the same time.