Well, you shouldn't trust any ADC you haven't calibrated and tested yourself. For 3 or 4 bits of precision, I bet it's pretty close to within 1 LSB. Though you don't know until you test it.
As far as the error-rate... I bet that could be fixed if you worked at it long enough, but losing .05% of the data stream is acceptable for some applications, like some basic audio work and as a basic oscilloscope.