If you're hunting for a legit Ben 10 Omnitrix watch, your best bet is checking out big retailers like Amazon, Walmart, or Target—they usually stock official merch from Cartoon Network. I snagged one for my nephew last Christmas, and the packaging alone was a nostalgia bomb. The watch had all the alien icons and even made those iconic transformation sounds! Just be wary of sketchy third-party sellers; some knockoffs look convincing but break after two plays.
For collectors, eBay or Mercari might have rare or discontinued versions, like the original 2005 model. Prices can get wild, though. I saw one 'Ultimatrix' replica listed for $200 just because it was 'lightly used.' Comic conventions or local toy expos are also gold mines if you prefer hands-on shopping. Either way, read reviews and compare prices—don't let hype drain your wallet.