FWIW, I have been using a TA01 for many, MANY hard use years, and been extremely pleased with the unit. It has never changed zero, no matter how much it got banged around. After about 20 years of use, the tritium was a little dim, so I sent it in to be recharged. IIRC the tritium continued to glow brightly enough to serviceable for about 50% longer than I was told to expect, so I was very pleased with that..
Although calibrated for 55 grain bullets, I found my TA01 worked great with 69 grain bullets too.