That is discontinued, but that does not mean it is bad, just that Garmin has made some later models.
https://www.garmin.com/en-US/p/518046/pn/010-01508-00
There are cheaper after-market mounts, but the Garmin mounts do not cost much more, you can get Garmin ones from non-Garmin sources.
https://www.garmin.com/en-US/p/11411#devices
I find that the mount is less likely to rotate around the handlebar if you wrap a bit of innertube rubber around the bar first. Then the zip ties and mount stick to rubber better than a smooth handlebar. You could try skipping the rubber first, the Etrex is lighter than my GPS, maybe that is not needed?
These types of mounts are prone to user error on putting the GPS into the mount. I always use a tether so that if the GPS falls out of the mount, the GPS is still hanging from your handlebar by the tether (cord) instead of getting lost somewhere.
I like the Ikea 2450 AA Ladda batteries, which also need a recharger. Eneloop AA batteries are my close 2nd choice. Or, use disposables.
If you get it and start loading different maps into it, best to put the maps on a separate Micro SD card (no more than 32 gb). The internal memory might be limited if you try to put several maps in it.
I know a couple people that have used an Etrex series GPS for randonneuring and I use a non-cycling GPS for bike touring and for randonneuring brevets.