First - be aware that you'll probably run into trouble buying ebooks from overseas, no matter what format you're buying. Not a problem if you're happy to buy before you go only, of course
I just bought a 2nd-hand PRS-300 - my only issue with it is the lack of SD card extensibility, which (to be fair) I knew before buying. But this MIGHT be an issue for you if you're travelling for a long time and don't want to store ebooks on your laptop. Otherwise, 450mb can take a LOT of ebooks, unless they're heavily illustrated or absolutely huge.
Hope that helps