vTaskSuspendAll stops the scheduler from switching tasks, whereas a mutex just suspends the tasks waiting for it until the mutex is available. In most cases, a mutex is preferable since it only blocks the few tasks that actually want the mutex, and doesn’t prevent non-interested tasks from running. You only want to ever use vTaskSuspendAll in those rare cases where you absolutely need the current task to continue running without being preempted by other tasks. Generally in a well-designed system these cases are all going to be inside the kernel - in FreeRTOS code itself.