It's mostly a monitoring / optimization thing.
The process of making a good espresso is:
1. Weigh the beans (w)
2. Grind the beans at (f) fineness
3. Tamp with (T) pressure
4. Extract (c) grams of coffee while timing (t) the extraction
Broadly speaking
the extraction should be c=w*2
the time should be t=c*1.5
If t actual !~= t desired, adjust f or T.
So what my doo-daad will do is:
a) store w, the exact weight of the beans so you can vary by +/- a few grams and not worry
b) record f, so you can put the grinder back to the same setting next time you use these beans
c) start the extraction, weighing the coffee and tracking the time
d) stop the extraction at the right weight
e) advise if the extraction was too fast or too slow
f) record all this for next time with the same beans, trends over time, tasting notes, etc.
It's basically replacing me watching the scales and counting seconds in my head and inconsistently writing notes on some paper near the machine.
People already buy scales with built in timers for this purpose or auto-dosing comes as standard on some £2000+ machines.
It's 100% not necessary; I've got no illusions that this is a killer product every coffee drinker needs. But it seemed like a fun project
. In terms of selling kits, I mean more or less at cost to other obsessive nutters like me who I know want such a thing because other people have hacked it together with arduino breadboards on reddit and other places.