The types of problems you describe with scales are common. I say that as someone that spent several years testing scales in shops and supermarkets, to be sure they complied with UK (and EU) Metrology laws, using test weights that had to be certified regularly by our local Weights and Measures people. We tested for things like repeatability (addng and removing weights, several times) and eccentricity (what happens if you put weights in different corners of the scale bed - are the readings consistent). And so on.
I say all that so you have an idea that my next comment is based on something solid, not just ‘online waffle’.
I too have a pair of cheap Amazon-sourced scales. I’ve had them about 5 or 6 years. I went through a full verification cycle with them, using those same calibrated and certified weights I mentioned, and they didn’t have the faults you describe.
In fact, the only issue I had with them (and it’s a nuisance for espresso making, but not insurmountable) was a tendency to be a bit slow displaying the weight accurately. What I mean is that they were accurate (or to be a bit more precise, accurate enough) and consistent, but it took a second or two to stabilise. So, I had to anticipate a second or two ahead of the reading when making espresso.
Oh, and one thing to watch for - scales are pretty damn sensitive. Don’t lean on or knock your work surface when using them. Even on heavy industrial work benches, someone just leaning on the bench several feet away would destabilise the reading, making it waver up and down.
Just to be clear though, I’m certainly NOT claiming every cheap scale from Amazon is up to that standard, or even that another identical unit from the same manufacturer would be, as my tests had a sample size of exactly one scale.
My point is merely that cheap scales aren’t necessarily inadequate for espresso..
That said, I’ve looked at Acaia (I think they were Lunar but it was a while ago) and been tempted, But I can’t quite get past the value for money issue. So … I haven’t tested them for those issues. I’d hope that at that price they wouldn’t have issues, but over time, those supermarket scales (which unsurprisingly given the use they got, were FAR more expensive than Acaia) did fail on occasion. Sometimes a good cleanout would do the trick, but sometimes, it required parts being replaced.
So I soldiered on with my cheap (£15 IIRC) Amazon thingy. I still enjoy the coffee though.
Oh, and as for the Bluetooth thing, I thought about that, but ended up with a pen and a sheep of paper. Crude, but effective. :D