I just bought a second one (a Salter digital) because my usual one (a Tanita digital) was acting out a bit. The old one is working fine now and though they both show different numbers (within 2lbs of each other) they both trend in the same direction at the same time, as in if I gain on one I gain on the other and the same with losing.
I weigh in officially once a week at my local pharmacy because it gives me a printout of my weight and I stick those in my diary. The weight I get there is smack in the middle of the two scales I have at home so I guess they're all broadly accurate