There are a bunch of weird smartwatches that get pretty close to this - for example, the Amazfit Bip S Lite claims 30 days of battery with a similar transflective screen (albeit I think the heart rate monitor drops to once every measuring 5 minutes in battery saver mode).

Similarly, the Withings Scanwatch claims the same, although as a hybrid smartwatch, it is not driving such a power-hungry screen.