Of those I’ve only had vivoactive 3, which I have atm.
I don’t use Glonass, just standard GPS, picks up a signal pretty much as soon as I walk out the front door. The touch screen can be locked to avoid false activation, so that shouldn’t be a worry, I have mine set that it locks automatically when I’m doing an activity.
I think they’re way better value than a dedicated cycle computer, as you can do so much more with them. Don’t be fooled though, the HR is only good for resting HR measurement, I use a chest strap for actual exercise as it’s way more accurate.
One very good aspect of the Vivoactive 3 is the accuracy of the elevation, I use it as a maker when hill walking, it’s never been more than 5 metres out, brilliant on an unfamiliar hill in the clag.
I looked at the 45 but it didn’t do floors climbed, which I kinda like tbh, not a biggie, but still.
There is a huge array of Garmins now, it’s no easy picking tbh. Best idea would be to write down what you defo want, and find a comparison chart.