If a customer enters an incorrect email address/phone, they will instantly see a corresponding message. No need to submit the checkout to validate the data.
Provide your customers with short points why they need your product. Add reviews, ratings, key benefits to persuade customers to complete the checkout.
You can pre-select a shipping option that will be default on your checkout.
Checkify, like any complex tech solution, is vulnerable to unexpected errors. If that happens, your customers will be redirected to standard Shopify checkout.