its certainly worth trying. its less server heavy as spamassassin, my friend uses a name for spamassassin as serverassassin. but back to business.
it uses also same procmail als spamassassin do, so it would be a minor implementation in ispconfig to get another checkbox for spamassassin and spambayes.
these days i had out of 500 mails 350 catch by spamassassin and the other 150 were scored as 0, even i let spamassassin learn these emails they still come through. while spambayes catch also these emails.