I have done like 1,000,000 Hanna Alk tests. I have very little problems with consistency. Only a small deviation from bottle to bottle. The number is never off by more than 0.5 dKH.
If you think about it...the "perfect number itself" really doesn't matter. For example... 8.0 or 8.5 dKH really doesn't matter. The tank fluctuation is what really matters. I test every night about 8pm.
If you test and it's 8.0 dKH on Monday night and test again Tuesday night and it's 9.0 or 7.0 dKH…this is when you should get concerned. A batch to batch 0.2-0.5 deviation only frustrates you on the last test of the old bottle and first test of the new bottle. After you get the new number...which may be 0.2-0.5 off from the old number it will not deviate from there unless your tank is growing, being over-dosed, being under-dosed, or you're not swirling the bottle. If you don't swirl the bottle a little before each test you will get weird readings at the end of the bottle because with anything....stuff settles out on the bottom. I like to tank the tip of the syringe and give it a quick swirl or two before I aspirate the reagent.
Now...if you're like
@Cody and test at 7am one day and test at 6pm the following day and wonder why you're dKH is off by 0.8....I'm sorry....I can't help you.
All BS aside....Hanna is quick, simple, and accurate. I trust my tank with it all day. Same with the Hanna ULR, Copper tester, and Salinity Pen.