Kai, I was worried too the first time I heard about them. But if you avoid the ancestral lands, you don't need to be concerned. Check the wiki to learn about which regions this includes: www.glitch-strategy.com/wik...
I do think the benefits of the ancestral lands are worth the risk of bandits, though. The Ju-Jus move quite slowly, and unless you get hit by lag it's not too hard to jump over them.
They are slow. Just hop along to the next street. They also announce what they are after, "I'm coming for your paper!". A dire threat! If you love your paper, run for your life! They do also take valuable items so beware. They are not hard to escape.
Yeah, you need to watch out for them, but traveling through the ancestral lands can yield a bunch of booty!! I got a focusing orb and two purple snow cones walking around there today! :-D