Have you found this device to be convenient to work with ? I am thinking of buying some of them.
If the units are such that the accelerometer values are varying by +/- 0.1 m/s^2, then you are getting 1% accuracy.
"but the X and Y are always a little (+- 0.1) off of zero," You can adjust the raw readings ( scale and offset ), so that the adjusted X and Y are actually zero , when the device is actually motionless on a level surface
If the units are such that the accelerometer values are varying by +/- 0.1 m/s^2, then you are getting 1% accuracy. That is actually pretty damned good, and you can't hope to do much better with an inexpensive accelerometer.
Thats actually a spurious comparison. It's only "1% accuracy" with respect to gravity. Which is fine, if that is all your are interested in. An error of 0.1 m/s/s in the acceleration of, say, an automobile, is actually quite a big error.