This work presents three techniques for 3D manipulation on mobile touch devices, taking the specifics of mobile AR scenes into account. We compare the common direct manipulation technique with two indirect techniques, which utilize only the thumbs to perform the transformations. The evaluation of the manipulation variants is conducted in a mixed reality (MR) environment which takes advantage of the controlled conditions of a full virtual reality (VR) system. A study with 18 participants shows that the two-thumb method tops the other techniques. It performs better with respect to the total manipulation time and total number of gestures.