A checked invoice is worth more if you keep it: the operator may file its key later and turn an open check into a finished one, refunds have a deadline, and two euros are not worth a letter – twelve sessions with the same provider are.
Everything stays in this browser. Neither the invoices nor the records nor the amounts reach the server; this page fetches a single value from it, the state of the register, and that is the same for everyone. The price is plain: clearing browser data means losing the archive. The export below is therefore not convenience but safekeeping.
The file holds the whole archive including the signed records. It can be read back on another device; the same invoice is recognised and not duplicated.