I can't edit the original post, so will have to post a new one.
The device I bought on TradeMe is an Eken M001 Android tablet.
There is a new firmware version available for it that fixes some obvious bugs (YouTube is broken) and - apparently - gives it a good speed boost, as well as direct access to the Android Market.
The device comes with Android v1.7.2 (Eken versions) and the update is to v1.7.4.
www.slatedroid.com has some custom ROMs but the site seems to be overwhelmed, claiming it is 'too busy right now, try later' about 75% of the time.
I've tried to download the update several times, but haven't managed to get more than 30% of the update file so far.