It sounds like the Leslie's test uses less (volume) reagent and perhaps less pool water. I wonder if you doubled the "recipe" in the leslie's test if the results wouldn't be closer. That's just a guess but may have some merit.
I have never compared the Alk test results of the TF-100 with other tests....might be interesting to do.
If a pool store is close by, and they don't use strips, you might get a third opinion although I would trust your own results over most pool store testing.