The PB903 has multiple tabs - there are some videos comparing brwosing with PB903 and Onyx M92, you can look at them either here:
http://baach.de/Members/jhb/-compari...-onyx-boox-m92
or from post 78 in the first thread in the Onyx subforum - I am not sure whether he tries to open several windows. In teh PB903 (and I suppose in teh M92 too) you can also view in landscape mode. Bear in mind that videos won't work. Enjoy!