I’ve just gone down this rabbit hole so I have a few thoughts that might help:
The vast majority of these scales send an electric signal up one leg and down the other. As such, they’re not really detecting your full body composition. They make an estimate based on your composition from your feet up to your pelvis.*
*It’s funny to weigh yourself before and after taking a dump to see your “muscle mass” has reduced by 150 grams.
There are more expensive options that come with a little device you hold onto which runs the current from your feet to your hands - these are meant to be better than just the feet, but they are significantly more expensive. And even these aren’t particularly accurate when compared to a proper DEXA scan (but it’s not like you’re going to do one of these every morning).
Having watched a bunch of YouTube reviews from various fitness bros, the general consensus seems to be to get the cheapest scales that do what you want, and then just be consistent with daily weighing at the same time of the day etc. As long as you don’t take the readings as gospel and just follow the trends over a period of time, they can be a useful tool - just take all of the “body composition” data with a pinch of salt.
Something else to bear in mind is the size of the scale and the method they use to send the electric signal.
The basic ones are 28cm square and have four electric pads that you have to stand on for the body scan to work. More expensive options are 30cm square and have an ITO coating which means you can stand anywhere and it will still work. I was concerned that 28cm would be too small and that it would be a balancing act to hit the four spots properly. But actually, for my size 8 feet, the 28cm non-ITO option has been fine. I think if your feet are size 10 or bigger, then the 30cm size would probably be better.
The final thing to consider is the app that comes with the scale. As far as I can tell, they’re much of a muchness, but brands like Whitings are meant to be the “Apple” of the smart scale world, so you would assume their app is better than the cheaper alternatives.
I narrowed my options down to the Eufy P3 (as I have other Eufy products that are good) and the Renpho Scales for Bodyweight. The Eufy comes with the bigger platform, ITO coating, a more current app etc. and apparently measures more metrics, but it’s three times the price of the Eufy.
In the end, for all of the reasons above, I went with the Renpho and so far, so good.