The Bayern-Ticket (as well as all the other state-specific tickets offered throughout the country) is a great deal, especially if you're riding multiple trains in the same day or have multiple people. It's good on everything within Bayern that's not high speed rail (S-Bahn, U-Bahn, bus, regional bahn) and for every additional person you only must add 5 Euros.
Just remember when you go to Salzburg you cannot use the high speed trains that link München to Salzburg, that means no Railjet and no Eurocity. You can *only* use the Meridian trains, marked as an M on the DB website or the DB kiosks. It doesn't take that much longer that the high speed rail, just be sure you don't get on the wrong train.
If you have any questions just ask the DB office at München Hbf, they can assist you with which trains you need to take, or feel free to send me a PM.
