Two Presence Detectors? - Classic and New App (May 2019)

I recently turned on on my new ST app the “Allow phone presence detection”. Now on my classic app, I have two “things” named Rey (from classic) and Rey’s Pixel (from new ST app).

A few questions:

Which one is more reliable? For me, it looks the same as far as activity. For my wife’s phone (GS9) the new app is more accurate. Any thoughts?

This bring me to another question: Do I need to have both apps on my phone? If I do, does my wife need both apps too (she really does not use the app at all)