I don’t have comparison with Dexa scan but I had some model of Tanita and I have Withing right now. I had both for a while. My Tanita readings were lower in terms of BF but the difference wasn’t significant. Tanica ~9% Withings 10%. My nutritionist scale (I don’t know exact model but it’s some certificated body analizer) always from -1% to -1.5% in comparison with Tanita. But…I notice (at least for me) readings are different in different time of a day and other factors are significant too (amount and quality of sleep, what I ate before, how much water I drank etc.). So, again - at least for me - those scales are useful only to track trends and there is always some error rate.