I think 10% is way out of the norm - something's up with either your install (eg correct wiring) or your device (eg software bug).
After a lot of effort on my part, I was able to figure out that our nighttime consumption was almost perfect; our daytime production (solar) and consumption is about 3-4% underreporting, both due to an error in the solar production calculation by Sense. These are based on twice daily meter readings, pre-sunrise, post-sunset.
Before the voltage correction in December, I was 10% off across the board - and I was ready to send mine back. I can guess my numbers closer than 10%.
Even with the lower error rate, I'm still torn. I think getting these numbers right is perhaps the most important thing Sense needs to be doing right, given device discovery is a slow and imperfect process I'd at least like some useful information.
edit and the reason I'm torn is because it's obvious the correlation problems are diverse and widespread, meaning this isn't a simple fix involving some software correction you can push to every user, and surely wasn't entirely corrected with the "voltage fix" in December. What that means is that it'll be incredibly difficult to fix for everyone, and from the looks of it, promises to be fixed for no one. I mean, I've had my device since November and have been vocal about the errors from the start. Very frustrating.