Enhanced Magento Checkout Process in Magento 2

We received a request from a long-standing client. He needs to rebuild his website. At this time (the end of year 2016). Magento version 2.1 has been working relatively stable. And we chose this version to working in this project. We spent 3 months working on this project. It involves a lot of work
 + Design new layout for new website
 + Convert PSD to Magento 2
 + Import Product from old website Magento 1.7 to Magento 2.x
 + Import Orders to new site
 + import Customer to new site
 + Setup server and move website to live.
 + Setup payment method
 After we have done all the work of this project. His client can now place orders through the new website. But we face the problem that Checkout Process on Magento 2 working a little bit strange with old website. You can see detail how to magento checkout process working on https://www.magebay.com/forum/magento-checkout-process/
 We made the decision to Enhance Magento Checkout to One Step Checkout Extension. The customer actually has a better experience in the new checkout page. they can easy to fill their info shipping address, billing address, or update their cart. Our client website: DIEGOS.COM