Yes, Rockchip players are multi-tasking, you can play music and browse the menus at the same time, they are capable of playing quality Mp4 (.avi ) movies) and have a miniSd memory slot (up to 2GB). the music quality is very high and they are stable (no problems with lockups or crashing)
Screen sizes are 220x176 (2") and 320x240 (2.2"), Built in memory sizes tend to be 1GB to 4GB.
Don't know if any are available from Ebay as I try to avoid buying anything from Ebay unless I really have to. There are a few on Uxcell and the prices are less than ebay prices.
In all you get a very good player for very little more money than a cheap ipod clone.
Link:-
Uxcell