Not that accuracy is the problem, but speed. I know that a beam borer with a good sharp bit will bore surprisingly quickly through quality timber, but I really don't know that I could match the speed of a German mortiser. That may be because I don't know all the "tricks". What do you find to be your most expediting techniques with a beam borer?
And yes, there is no comparison between the speed of a cross grain mortiser and the Makita. I would say the Germans are two to three times as fast. I still like my Makita to take to jobsites though.