I've not used one personally, I've read mixed results about their xbmc abilities though, some are usable Abbas others less so, is there any particular one you was after, I'd Google particular models to see if there's any feedback on its use with xbmc before soothsaying cash on one
The one for XBMC is the Pivos XIOS DS, that is the official Android box for XBMC. Anything else is not supported though it could run it with the right hardwawre but your on your own. Pivos forums is where you will find XIOS users & downloads for XBMC.
It's comparable to XBMC running on an AppleTV but without the need to jailbreak and more media support.