I've mowed my own yard by headlamp a couple times. Two things I've noticed:
1) Low color rendering index (CRI) light and very blue tints can make it very hard to see fine details in the grass. Compared to what I was using at the time, the standard CRI models from decent manufacturers are a step up in color rendering, but my preference would be a dedicated high CRI.
2.) Headlamps, being close in line with your vision, don't shine at an angle that lets you see much shadowing. This can make the difference between cut and uncut grass or subtle contours of the ground much harder to see. I think having a light mounted to your mower in addition to a headlamp would be helpful.
With the first point in particular in mind, the Zebralight H600Fc or H600Fd are perhaps the best option. The F600Fc produces a slightly warmer light (but not quite as warm as a traditional halogen automobile headlight), and would be my personal preference. The H600Fd should be very neutral in tint.
The Armytek's have a very rugged build. They don't state the CRI for most of their models like Zebralight does, but seem to be pretty good. I've been happy with mine functionally, but I know several other members have experienced quality control issues and had to have them replaced. I suspect if you don't get one with a problem, the Armytek's will stand up to a lot of hard use. The main reason I lean towards Zebralight for your use is because for the H600F c/d, I know they are very selective about the color quality of the light.
By the way, since you mentioned lighting up a shore 1/2 mile away - around here we talk about "throwers" and "flooders" a lot. Throwers have a tight "hot spot" in their beam designed for providing useful light at long distances. Flooders have broader beams good for lighting up a wider area at shorter distances so you can provide even illumination across most of your field of view. Both the Armyteks and the the particular Zebralights I mentioned are flooders, but with the power that 18650 batteries can produce, do so at pretty decent distances.