Yes, you can manually change your default search engine using this url. Substitute %s for whatever your query string variable is for your device/browser.
https://zapmarks.io/u/%s?api_token=your-api-token-here
On Chrome, you can simply install our extension which allows you to type 'z {keyword}' to access your Zapmarks. Other native browser extensions are in the works as well.
https://chrome.google.com/webstore/detail/zapmarks/pdomgldhp...
We have a few benefits over the competitors, like Secret Access Links which allows you to use your Zapmarks on new browsers and devices without logging in.
https://www.youtube.com/watch?v=fr4dPcnrUMM
Also, we are working hard on developing lots of other ways to integrate our product into other devices and platforms, like Alfred on the Mac.
https://s3.amazonaws.com/graftechnology/zapmarks/Zapmarks.al...
Hope that answers your questions. Thanks!