I want to buy an Apple Watch to track my heart rate and number of laps as I swim, and that's it. The reason I'm choosing the Apple Watch as a fitness tracker is that looking at the graphs on the youtube channel The Quantified Scientist, it looks like it is a lot more accurate than any other wrist-worn device, and a few percentage points off can give a very wrong heart rate reading. My primary phone isn't even an iPhone, I just have one lying around to activate it with. I haven't found any other comparisons that are this in-depth. But it's difficult to understand the software without having one, so I just want to make sure I can swim and look at my wrist and see both my heart rate and number of laps in a 15 yard pool. Also, it looks like every Apple Watch in the last several years has the exact same heart rate sensors so I can just go with the cheapest SE or whatever. Is this correct? Thanks.
with the stock app, yes. with a third party app like Workoutdoors, you can have a much larger range of metrics to choose from and display.
i would keep in mind, though, that optical heart-rate sensors do struggle with getting readings while swimming in water and Apple notes that you may not get HR readings for swimming workouts.