I'm late to the party but my two cents... I'm a sucker for consistent data. I bought two scales from Walmart, glass top (more rigid for better consistency), I weigh on one and verify on the other. The verify scale normally reads .2-1lb heavier than the weighing scale. If I get a variance greater than that I recalibrate both scales.
For composition I get DEXA scans. My first scan was supposed to be my starting baseline but the DEXA folk scheduled me ~45 days out and I lost 21lb during that time. Since then I've lost another ~20lb and got another DEXA. I plan on getting another in another ~20lb and how my trend maintains will determine the interval for the scan after that. I'm ~50lb from my optimistic target weight that should have visible abs. I plan on getting another DEXA once I'm steady at my target/goal weight, then another if I have a meaningful recomposition phase after that.
For me, impedance scales don't offer the repeatability I'm wanting, so I pay the money and drive an hour away for the DEXA scans.