I'm new to the world of ph and ec/tds, but in my opinion dont rely on a factory pre-calibration. I calibrated before first use and indeed it needed adjustments. I have recalibrated every 2 weeks or so, and while nothing has drifted too far, I have had to adjust a bit the low setting.

Also make note of which solution yours came with so you can buy the proper calibration fluid for EC/TDS. Some use 1500ppm solution, others use an EC rated solution.