From what I've seen, the techniques are almost identical, with slight differences in position. The difference is the emphasis of each. JJJ is more variable, different schools will have different emphasis. So some schools focus on striking more and others throws and still others focus on groundwork more. BJJ is consistently groundwork oriented although the syllabus does contain a lot
of standing material including stuff taken from wrestling (most of which incidentally is also
found in JJJ but for some reason seems to be less used)
As to exercise, while my Scottish Dojo is quite light on the exercise, my Singapore Dojo is very heavy on training for strength and endurance (although this is not done quite so much in class) the Dojo has a small gym with weights, etc and students are free to use it any time. So you see, even this differs between different schools. What you get when you enter JJJ is basically luck of the draw.