If you have a smartphone that it can connect to, there's not really a reason to buy a separate unit (well unless you're just looking for an excuse to buy one anyways). Just use one of the numerous smartphone apps suggested. No matter what you use, you'll need to have a connection to the internet (either cell network or satellite network) and that means paying money for it. With your cell you're already paying for it (and tracking uses very little data).

Battery life is going to be a concern for any live tracking device, but you can buy an external battery to hook up to your cell phone for around $25. Like here's one suggestion that's 10,000 mah (the built in battery is usually 2,000-3,000mah) -
https://www.amazon.com/Anker-10000mA...ds=usb+battery

You hook it up to the usb port on your phone and it keeps it charged.

I would mention one other safety device that I've seen a lot of people mention before - a highly visible helmet camera. Here's one suggestion that's orange and highly visible:
https://www.bhphotovideo.com/bnh/con...=REG&A=details

No activity is risk free, a house near where I work had a gas leak and the entire house blew itself up. It was crazy. Every day you get into your car you could get hit by a semi. Nothing is without risk.

Sometimes you run into the small number of people who are just ********, who want to hassle cyclists. Having a helmet camera makes them a lot less likely to act on it knowing that you'll be able to show the video of what they're doing to the cops or in court. If you're looking for a safety device, I would skip buying a garmin (use your cell phone instead) and buy a visible helmet camera.