I think you are over-analyzing it. Ask your pharmacist for one from a major brand company that is easy to use. No machine for home use is "perfectly precise." Even the ones used in hospital intensive care units will give a different reading 5 minutes apart. That's just the way blood pressure measurement is.
The important thing is that you use it regularly in the same way each time so that you can see trends over time. Is it increasing over time? Or is it going down over time? Does it spike at certain times or day? Does it tend to be up when you eat more sodium? Does it tend to be down when you have exercised regularly for a while? etc. Any major brand should be accurate enough to tell you that.
I recommend getting one with a digital readout. There is an art to reading a gauge and listening through a stethescope like the old-fashioned devices require. Even professionals struggle with that skill. Get one where you put the cuff on, sit still, inflate it, and wait for the result to show up. No skill required.
You can either get one that inflates automatically or that you pump up manually. The manual ones are cheaper, but just as accurate. I use a manual and appreciate the hand exercise of pumping as I broke that hand a few years ago. :-)
Finally, make sure you use the right cuff size. You should be able to fit it snugly, but should not have to struggle to do so. If you are obese, you might need to get a larger cuff. The machine should come with some recommendations for putting the cuff on and being sure that it is the right size.
I got mine in my local pharmacy almost 10 years ago for $25. I check my BP twice per day and have only had to change the battery a few times. I record in on a little flowsheet I make for myself each month. That way, I can see the trends up and down as I maintain (or fail to maintain) my healthy lifestyle. No need to spend a lot of money or make it more complicated than it needs to be.