I bought this watch for my wife to track sleep, and walking, biking. She wanted a small size (40mm or smaller), and there are only a few options of Garmin watches in this small size.
Compared to the Vivoactive 4S (the Vivoactive 5 has no "S" size), this one has the Elevate 5 sensor on the back, which supposed to be more accurate, and it has voice call via the phone bluetooth.
The call feature sounded like a gimmick first, but my wife actually likes it. She mainly uses it at home, or outside when pushing the stroller. It is useful for quick calls with family members.
The interface is a bit confusing with the touch and the buttons. When has to remember when to swipe, touch, and when to press the upper or lower button. And the third button in the middle doesn't make any sense at all. It should have five buttons in the same locations like the Fenix (three on the left, and two buttons on the right), or no buttons at all.
The watch is a bit thicker when wearing it compared to the Vivoactive 4S, but still manageable.
It is a bummer that it this (very high) price point it still doesn't have flashlight, I would have expected that.
It has ECG, but ... any dedicated device measures it betters, and cost only €100. I wouldn't choose this watch for the ECG function, if you need ECG, get a dedicated device, which is calibrated and works well.
All in all, a good watch, but it's too expensive (€420) for what it does, it should cost 50% less.