Assuming the home test counts for your driving licence
Licence vision certificates must come from centres accredited by the licensing authority, which file results electronically — a standard home visit is not that. People pay AED 150–400 at home, then discover they still need the approved-centre test. Use the home visit as preparation, and ask about accreditation before booking if the licence is your whole reason.
Accepting a verbal prescription or a 'we'll make your glasses' promise
Without a complete written prescription including pupillary distance, you are captive to the tester's own glasses pricing. The written document is what makes the market work for you — any optical shop can fill it. No paper, no payment.
Waiting for a child to complain before testing
Children rarely report blurry vision because they assume everyone sees the way they do; the signals are squinting, sitting close to screens, and slipping schoolwork. By the time a child complains, myopia may have progressed for a year or more. An annual test through the school years is cheap insurance against exactly this.