I had an Apple Watch 4 for years; eventually the side button gave out, and I lived with that for a while, but decided to treat myself to a new one and got an Ultra 2 (so, not at the cheap end of the spectrum). The big attraction of the Ultra to me is that it has 2x the battery life. I can get 3 days between charges; I could probably get more. Charging it for the duration of a shower is enough to prolong that. As noted, this is nothing compared to a Garmin.

It's useful to think of the Apple Watch as an iPhone peripheral. The watch specifically needs to pair with an iPhone (not even a different Apple gadget). Heart rate, despite what crazyravr said, is accurate. Comparing it against a chest band showed the two were the same, sometimes with one lagging the other by a second. It's not great for sleep tracking—it's inferring your sleep state from the noises you make, your body temperature, your heart rate, and your movement. So I've had a couple of nights where my brain was spinning but it showed as a decent night's sleep.

Some years ago, I had a Fitbit, and it would automatically track activities. If you go for a walk, it will notice that and record it as a walk. With an Apple Watch, it will notice you're going for a walk, and after 14:45 alert you: "It looks like you're going for a walk. Do you want to record it?" You need to give it explicit instructions. And there's some stuff, like yardwork, that could count as a workout but that movement pattern hasn't been modeled, so the watch won't pick up on it. You can explicitly start a "mixed cardio" workout though.

I probably get more benefit from it as a convenience (it's nice in the kitchen to raise my wrist and say "start a timer for 20 minutes named 'potatoes'.") than as a fitness tracker. If all I wanted was a fitness tracker, I'd probably get one.

FWIW, here's a comparison page for the SE, 9, and 10 . Also FWIW, bands are interchangeable between all Apple Watches.