The 900 motors from this seller were the end of a batch which his main company purchased to manufacture golf trolleys. Grade A motors from this batch were purchased and resold by Marks Model Bits and ACTion, who had the last two trays. These cheaper motors were water-damaged, having been left in a leaky outbuilding, and were sold on E-Bay through his daughter's account.
I know that the particular model of trolley for which they were bought is no longer in production and so I very much doubt if there are any more left - damaged or pristine. With a minimum order quantity of 10,000 from Johnson, the motor manufacturers, I'd also doubt if such motors will be available at such a low price in the future. It looks like we're all going to have to wait until Graupner get some more of their Speed 900s next year.
As regards the speed controller in question, it seems that if you get one that works reliably then you're lucky. I certainly wouldn't use one with a Darke Horse 785!
DM