My Tee2+ consistently reads higher than my GlucoRx-Q. Typically anything between 1 and 2 mmol/l. My Rx-Q ranges are generally low 6's to mid 7's - I never see more than an 8.5 unless I've been very naughty carbs-wise or sample less than 2 hours after eating, yet I've had a 9.9 out of the Tee2+. That's parallel testing from the same blood sample, and alternating between testing first with one then the other, in case reading with one could skew the result of the other.
The figures I'm getting from the GlucoRx-Q are more consistent with my latest HbA1c result, so I'm inclined to trust it more. It's a shame, because the Tee2+ has better functionality in most respects, better reporting software, and cheaper test strips. I tested the Tee2+ with both test solutions and it landed pretty much in the middle of the range for both. I've tested the Rx-Q previously, and it did much the same.
+/- 15% allowable error 98% of the time, these things are basically random number generators roughly centred on your blood glucose. A level of 6.0 can legitimately read as anywhere between 5.1 and 6.9. And those are massive differences in blood sugar control.