Switching is an hour, not a project
Wherever your stock lives today — a spreadsheet, a notebook, your till’s stock module, or another inventory app — getting it into INV3NTORY is one CSV import and one till connection. Your till (Square, Zettle, Lightspeed, EPOS Now) stays exactly as it is, and everything exports back to CSV at any time, so there’s no lock-in in either direction.
Most shops are live within an hour: import your products, connect the till, set minimum levels on your fast movers.