Benefits

The RB Guardian has many benefits most of which relate to safety and improvement in dive liberation.

Safety

Minimises task loading by removing the need to monitor handsets regularly, because pp02 levels are being monitored passively at all times, minimising stress loading on the diver.
Eliminates danger of divers getting sidetracked during dives and forgetting to monitor handsets often enough.
Provides real-time warning of pp02 level, even in poor/impaired visibility conditions, such as low visibility and low ambient light.
No single point of failure*. Patented approach consisting of doubly fault-tolerant and fail-safe electronics ensures that any one or two failures will result in either fail-safe mode or continued operation. There are no failure modes for this device that wouldn't fail in a manner instantly noticeable by the user (i.e. fail-safe). *Except power supply which fails-safe.
Safe continued use of rebreather if controllers fail. In the event of a controller (or dual controller) failure, the Primary HUD can be used to let the user safely manage optimal pp02 via manual Oxygen injection and Primary HUD signals.
Calibrates at same time as rebreather to maintain tracking between rebreather and HUD.

Does not rely on rebreather controller electronics or rebreather batteries and so is independent of controller failure. If the rebreather fails in a manner that it disturbs all three of its cells simultaneously, the RB Guardian will show the disturbance but will not provide accurate pp02 readings as it uses the same cells.
Can complement a rebreather's handsets and audible warnings.

Improves the dive experience and enjoyment, because equipment management/monitoring is minimised. The Primary HUD allows the diver to passively monitor the rebreather and reliably draws the diver's attention to any pp02 problem with it in real-time and at an early stage in the problem's development. This enables the diver to enjoy the dive as opposed to monitoring their equipment, which should only be necessary if there is a problem with it.
Supports task-oriented diving. Particularly beneficial where tasks are to be performed during the dive since it allows the diver to concentrate on the task without the distraction of pp02 gauge monitoring. It further avoids the possibility of forgetting to monitor the gauges or not performing the task properly due to regular gauge monitoring.
Removes the pp02 awareness problem. By mounting the display in the diver's peripheral vision, the diver does not even have to look at the display to know they are breathing a safe gas. The display can be seen at all times without needing to look at it. Divers are provided with full confidence in their abilities to always be made aware of unsafe pp02 levels.

No need to have to remember to check gauges, because the HUD alerts the diver when it is time to inject.
By maintaining a narrow range of operating pp02 via the HUD, the rebreather can be run more efficiently and decompression times can be minimised compared to normal operation. This makes KISS style units much more competitive with controller based CCRs in optimised decompression terms.