Is the main one the fact that kaju incorporates boxing (western or Chinese or both??) as well? What other differences are between these two arts in terms of their general approach/philosophy and the kind of moves they tend to use?
I saw your other post about kajukenbo. You are unlikely to find many older schools (koryu) of Japanese jiu jitsu in Europe. I have only ever found 1 koryu school locally, and it was sword orientated. Koryu schools teach specifically types of jiu jitsu with armor and the medieval Japanese battlefield in mind. Most of the "Japanese" jiu jitsu in Europe is "gendai" meaning modern. Usually created post 1950 and usually a mix of karate and judo and usually not in any sensible way as these folks are rarely pressure testing against skilled opponents.
With regards to them not pressure testing against skilled opponents, I've heard that the only except is Hokutoryu Ju-jutsu which was developed by a former boxer. Do you think this might be the case?
Hokutoryu Ju-jutsu is a gendai and not Japanese jiu jitsu - its Finnish jiu jitsu. A big part of pressure testing is testing against people not within your style but under a relatively open ruleset e.g. K1, ADCC, Unified or Pride rules. Testing within your own style often leads to bad feedback of the tactics you should develop.
