I own coffee shops in the Midwest. Feel free to ask me any questions.
Flat Burrs: popular amongst 3rd wave coffee shops. Their burrs produce similar fines (particle sizes). Predominantly this type of grinder is only popular in USA.
CONICAL burrs: this is proper way, to pull an espresso. Will not find a single coffee shop in the whole of Italy using anything other than conical burr grinders due to the fact these burrs produce two shapes of fines (particle sizes), which is important. The smaller of the two fines slows down the extraction, allowing the big fines to really have all the goodness extracted out of them.
Important note: conical grinders are always the commercial equipment most expensive model. We use a Mazzer Robur S in our coffee shops, and it is easily the range topping grinder from Mazzer in Venice, Italy.
What any coffee drinker should be primarily concerned about is not so much equipment as discussed here, but bean oxidation and its major contributing factor to “flat/dead” espresso shots. Just like when you cut an apple, and let it sit on the counter to turn brown (oxidation), the same
Happens to roasted coffee. You just can’t see it because the coffee is already roasted dark.
Conclusion: as a coffee shop owner who imports his coffee himself from Rome, Italy. Prioritize freshness of beans (oxidation NOT roast date), a bag of beans, once the bag is opened, will fully oxidize in about 36 hours. Next time you go to grab an espresso, ask to see the shot’s immediate after extraction, if it does have a head of Crema on the top (like a Guinness Beer), it’s stale beans AKA a flat shot, AKA garbage!