The source code is an Open Source software. It is open for anyone to understand, extend or improve. And it is free!
Advantages of an Open Source software are:
You can choose to change your service provider anytime.
You can host the application anywhere, including your own server to gain complete ownership and privacy of the data.
You can access a community to support you, incase you need help. You are not dependant on your service provider.
You can benefit from using a product that is critiqued and used by a wide range of people, who have reported hundreds of issues and suggestions to make this product better, and this will always continue.
Alternatives
There are many Open Source ERPs you can consider. Popular ones are: