Thirty seconds, on a phone, with GST applied
Pick the party, pick the item, enter the quantity. The unit, rate, HSN code and GST rate all come from the item record, the totals build themselves, and the PDF is ready to share. There is no separate "GST screen" to fill in and no calculator involved, which is what makes it usable at a counter with three people waiting. Kg, ton, bag, piece, foot, box and CFT all work the same way, so a mixed bill is no slower than a single-item one.
Offline is the normal case, not the exception
Power cuts and dead network are facts of trading life in most of the country, and a billing app that stops when the signal drops is not a billing app. Bills, receipts and deliveries recorded offline sit on the phone and sync the moment coverage returns. Nothing is queued in a way you have to manage — you carry on billing and the sync happens behind you. Shops in Bhagalpur, Purnia and the hill districts use the app rather than the browser for exactly this reason.
The same account on the phone and the computer
Whatever is created on the computer appears on the phone and the other way round, immediately, because they are the same account rather than two systems that talk to each other. Your supervisor bills from the site, you see it at the shop. You add an item at the shop, he has it on the truck. Staff logins carry only the permissions you grant, so a billing-only login never sees your purchase rates or your profit figures.
What it replaces
For most shops the app replaces three separate things at once: the bill book, the udhaar register and the phone calls to the shop asking what the rate is or whether a party has paid. All three become one screen that everyone with a login is looking at. The practical effect is that the owner stops being the bottleneck — a supervisor at a site does not have to ring the counter to check a balance, and the counter does not have to ring the owner to confirm a rate. That is usually the change people notice in the first week, ahead of anything on the feature list.