The down sides of a traditional junk rig (flat panels
as opposed to the newer cambered ones) is that they have less than sterling performance to windward, more weight aloft, and lesser ability to as light air sails
Most if not all of these can be fixed with modern construction techniques and materials.
I think is was Bruce Roberts
that said something like, " a boat with a Chinese lug sail will go to windward as well as the HULL
is capable of."
All in all they sound like a really interesting way to go.
There is a really go section on the chinese lug rig (junk) in the Sailmaker's Apprentice. (there is a link to it on amazon on the suggested reading page on my blog)