Suunto Spartan used already whole season. Gps sensitivity can be adjusted till 1s., the screen is clearly visible in all weather conditions, actually do not have issues with touch screen mode, I think you can even disable it. Live track you can see on watch screen, the scale automatically adjusts depend the distace run, it help with orientation when you are fare from shore.
Doppler is a second way for the watch to compute your speed by listening to the change of intensity of the frequencies emitted by the satellites as the distances change between the satellites and the watch.
An illustration of the Doppler effect is for instance the sound of a fast passing train or formula one that get closer to you and then move away. You can deduct the speed of the car/train by the attenuation of the sounds they emit as they move away. It works the same with the frequencies emitted by the GPS satellite network. The watch then determine your speed thru an algorithm with both the Doppler effect Data and the GPS location. It’s real time and it’s much more accurate than only knowing your speed by the location only.
If you look at the watch that Alex Caizergues (world speed record holder in kitesurfing) was wearing on his wrist during his record you’ll see it is a GW60.