It is not available with a 4" outlet, you might try to add a 6x4 reducer to the branch. If you have any other inquiries about our Master Flow products please call Technical Services at 800-211-9612.
Tee Saddles are used for when the duct is the same size ie 6" from a 6" duct. For this application you would use what is called a takeoff which can often fit a variety of larger sizes ie 8" to 20"+
don't know about flex, don't think it will work