It appears "Low Power Mode" has replaced "Power Reserve" (which shut down all features except simply displaying the time)

Use Low Power Mode on your Apple Watch

I have a 7.

But I got excited about Low Power Mode after talking with a guy at our Apple Store who said it was better than Power Reserve and would behave like LPM does on my phone (comes on automagically when the battery drains to a certain amount). Said it could make the battery last twice as long between charges.

I came home, thought about it, and bought the 8.

Now that I have it, I know it DOESN'T work that way; the only way it turns on is manually, and that's not helpful to me at all.

I don't see how LPM is a better feature than PR was, and given that it's the main reason I upgraded, I can't think of a reason to not return the 8.

Can someone clue me into what I'm missing?

Cause right now, I'm thinking there's no reason to keep the 8 when my 7 works a charm, and PR seems "better" than LPM.