Hi Amorphophallus,
I bought a seed in 2004 at ebay from a British seller ( tropical-world ) and the tuber is now 14 cm across, 9 cm high and weighs a little bit more than 1 kg.
It was of course grown under suboptimal conditions here in northern Germany; it is thriving in late spring/early summer and enters dormancy already in November/December.
But I am quite satisfied with it's growth. As you can see in the picture it starts to grow two offsets.
I do not think that it will flower this season.
Happy growing, Bernhard.