The screenshot you posted is from Coinbase commerce. Why not use that instead? Because unlike the website you're using, Coinbase can easily be implemented without the need of any technical knowledge, unless you're trying to make something customized.
Also, the website you're using has no online presence, and a lot of typo's. I don't think it would be smart to trust them with your money.
The only reason is sendbit allows me to have my private keys, any suggestions? what do you think? can you sign up and see if the system is good?