When designing an app is it better to hire a designer or ' rent' there services from a company?

I am looking to design a mobile phone app.

I have two options, one would be hire an app design company for a fixed price and launch the app.
Two would be to hire a developer on a salary.

Option one makes the most sense financially and would be easier. But if the app took off, would the developer i would inevitably have to hire have trouble reading the code from the hire company?

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia…).