The leviton box is also angled on one side. I used the angled side for the outlet side of the plate giving me more room for the LV cabling.
The gray box is almost exactly 3.5 inches deep. Also, the box is not old work, no tabs. It must be cut in right next to a stud. It comes with 2 screws and 2 places inside the box to screw the box against the stud.
I have mine installed into a 2X3 wall with plasterboard as the wall material and it just barely passes the back edge of the stud(2X3) with the front edge being flush with the exposed wall. Fortunately the other side was a utility/well closet with no back wall to deal with. It made installing it and cabling it a breeze.