the results from a probe are only indicative. What a probe will show is exactly what your senses should ascertain.
As stated many times in the past, the baby roaster is a sample roaster. Treat it as such and you will learn a lot.
I understand the results from the probe are only indicative and caveats are taken as such, but they have been very consistent and are indicative of what I want to achieve. I did try using my senses for probably much more than 40+ roasts (previous roaster was HG/BM), but it was hardly consistent for anything less than second crack - I get good roast sometimes and craps the other time. If that's what the Baby Roaster can do, I would have given up back then. I did also try taking notes and logging the milestones etc - it's not easy when you have to drive the roaster, control the flame, shake the roaster, take note of the timer etc. After logging(manually by note-taking) about 20-30 roasts I decided it's a worthless pursue - they're hardly consistent bean-to-bean - once I'm finished with a bean, I have to learn all over again.
Another few reasons for installing the thermometry - First, my sense of smell was easily overwhelmed and desensitized by the constant sniffing(not to mention headache). Second, I roast under a kitchen hood and am not comfortable in consuming the potential emission(diacetyl etc) produced from hi-temp roasting. Lastly, I couldn't get consistent result for lighter roast (I enjoy beans not roasted up to second crack) with different beans.
I'm just a home user - the baby roaster is my only and main roaster, and so I want consistent & predictable result. I found that installing the temp probe helps achieve that.
To give some ideas, this Peru bean I have currently absorbs so much heat that using the same setting barely bring it to first crack. The Brazil has a tendency to speed up after first crack, I wouldn't have known that without a thermometry and as such, can't take a proper measurement to circumvent that and will probably attribute that to bad bean quality. Peaberries absorb so much heat during first crack that my normal flame management would have caused a stalled roast - again, something we wouldn't know without some measurement.
To make it harder, I don't have a reference so I wouldn't know how a proper roast of that particular beans would taste like. I may achieve what I discovered by thermometry eventualy, but I would've probably chucked out tons of beans by that time - or accustom myself to drinking all those bad batches.
It's like making espresso - some swear by ballparking the dose, temp, and pressure. I don't doubt for a second that will work. But the only way to increase consistency is to have some proper indicators (by measuring them, but not get absorbed by the numbers).
Another advantage to newbie roaster(which is me!) is that - you can condition your sense of smell to the phase of roasting (as indicated by temperature). Without long roasting experience behind me, I do not know how drying phase, different development phase etc smell like - they all smell like roasting coffee, different but it's hard to tell. But to be honest, I don't like smelling them. Having myself smell like a walking roaster plant afterward is bad enough, I don't want to sniff them inside my body too.