Coupon-finding browser extensions promise to test every known code automatically at checkout, saving you the trouble of searching manually. We timed ten checkouts both ways to see how much that actually helps.
On speed, extensions won clearly. Manual searching averaged about four minutes per checkout (opening a new tab, searching, testing codes one by one). The extension ran its full test cycle in under 20 seconds on every site we tried.
On savings, it was closer than expected. In eight of the ten checkouts, the extension found the same best available code a manual search would have. But in two cases, a manually found code (one from a site like FitsAbroad that hand-verifies codes) beat what the extension applied, because the extension had an older, lower-value code cached that hadn't updated yet.
The practical approach that came out ahead overall: let the extension run first since it's fast and usually gets you most of the way there, but do a 30-second manual check on any purchase over $100, since that's where the gap between 'a code' and 'the best code' actually matters in dollar terms.
Extensions are a good default. They're just not a substitute for checking the big purchases by hand.