On Windows, you can have both versions installed simultaneously.
You generally won't use ODBC for building a modern web application backend (you’d use a native library instead). You will use it for: postgresql odbc connector
PostgreSQL uses Multi-Version Concurrency Control (MVCC). If your application is complaining about "concurrent updates," enabling can help the driver detect if a row has been modified by another user since you started editing it. On Windows, you can have both versions installed