I would say that for most aikido bokken training a good Japanese white oak bokken would be fine (the one in your link should do to start with). If however you intend to do a lot of hard contact between weapons you might want to move to something like one of the hickory bokken offered by
Kingfisher Woodworks. Definitely not on the inexpensive end but well worth the money, IMO, if you are doing a lot "bashing together"
You might also try:
The Kiyota Co.
2326 N. Charles Street
Baltimore, Maryland USA 21218
Tel (410) 366-8275 Fax (410) 366-3540
They don't have a web page but they'll send you a catalog with a lot of different choices.
I've never dealt with Kim Taylor at
Sei Do Kai but I've heard many good things from others. You might want to check out their weapons and/or weapon sets.
Bronson