Microsoft have released an ISO for Windows 10 Redstone 5 build 17744 for Windows Insiders. The ISO is available for Windows Insiders to perform clean installs of Redstone 5, and this build is good build for testing. It was released to the fast ring August 21st.
The ISO is available from Microsoft and is designed for Windows Insiders to test clean installs.
Here is my hands on video from when it was released to the fast ring: