Worn thrust arms - Dangerous?

[StephenVA]

There is a lot of basic brake info up on this site and on the internet that will help you determine the shuttering problem. If new pads were installed on old rotors with out "truing" the rotors first that alone could be your issue. A best practice is to replace rotors and pads at the same time as the costs are cheap. Quite a few owners have lots of success running two to three sets of pads per one pair of rotors. The rule of thumb is to measure the rotor thickness, replace as necessary and break in the pads correctly. If you try re -bedding the pads, your shuttering may go away as the pad material has not transferred to the rotor evenly.
An out of spec rotor is one that is not parallel on both sides or too thin. The thickness is stamped or cast into the face. As mentioned above a simple test using a dial indicator while the rotors are on the vehicle with the wheels removed. Takes 30 mins to confirm the status. Old saying in car repair world, Test, don't guess.