I joined one such tour 10 years ago. It was an enjoyable way to spend an afternoon outside of Salzburg.

At that time I used Rick Steves' guide book, which said that there were more than one companies running such tours, and the itineraries were very similar. So I just picked one that suited my schedule.

Perhaps you may go to your public library to find an up-to-date copy of RS' "Vienna, Salzburg & Tirol" guidebook to read his up-to-date review of those tours from Salzburg?

My brother and his family took Bob's SoM tour and enjoyed it.

BTW there a TV channel that plays the SoM 24/7.

FWIW this may - or may not - be of interest -

http://chicagoschlager.blogspot.com.au/2012_09_01_archive.html

Took the Panorama tour last Dec. Third time onver 40 yeasrs that I have taken SOM tours. Enjoyed them all. Be aware that you don't visit many places in the city. On the Trip Advisor Salzburg forum, LizR has described where to see many of the in town sites.

I took the Panorama tour this past November. There is a lot in Salzburg you can see on your own as we only drove by them, we never go out the van in Salzburg. Outside of main Salzburg they took us to Hellbrunn (you can take bus there and if you walk around you can find the gazebo, Leopoldskron palace, Lake Fuschl (this is my current profile picture) and another Lake area. The last place was Mondsee Cathdral. The tour was ok but I am not a big Sound of Music fan.

"and another Lake area"

That would have been a view from above St. Gilgen and the Wolfgangsee is the lake you saw. These are in the opening scenes of the movie.

I used the tour company where you get a discount by showing the Rick Steves book (I only take xeroxed pages of areas that I going to visit but that worked for all discounts).