1) Once you have your dirt recipe figured that things gonna collect dust.
2) With dirt you don't need to be bang on 6.5 here, you generally good between 6-7, better between 6.3 to 6.6 ish for our mixes in general, also need to factor in buffer capacity of water and ppm for ph drift, this could mean your soil optimum is now 6.0 to 6.3 ish.
3) Not all soils are created equal, you don't know if 6.5 is the right ph for a given particular soil type, ie calcium content, element antagonism, microbial activity. You know it works for your soil and nutrient regime, but what about mine? I've tested the outdoor soil here and its 7.5 upto 8.2 and it grows awesome because its alluvial soil ie a flood plain. So great you nailed 6.5, what does that mean for buddy next door.....not a pinch of coon shit.
4) You said it yourself, after four months you took it out and tested it. Set it and forget it, all your pots are the same soil typically, you do one you've done them all
5) That tool isn't meant for the average grower.
6) That thing isn't the holy grail of ph testing, meaning it's not what the use in a lab setting. The accuracy is +/- 0.1, resolution is +/- 0.1, I would call that to be ok, not great. It could very well be slick advertising and sexy looking product but underneath the same ugly redheaded step child that I'm using, all sourced from the same factory in China.