The timing receivers often have other advantages beyond just sawtooth, including stuff like being able to produce a time pulse with a single working satellite in view once their position is learned.
Should have clarified: previous generation timing receivers. Yes, self-survey + stationary mode + O/D mode where you can track a single SV and such, are essential for stable time sync, not just sawtooth.
There is an exception re. sawtooth, but only a recent one: the Furuno GT-100, priced between the ZED-F9T and the Mosaic-T, has 200 ps clock resolution and doesn't even provide a quantisation error output.
