I have Venz V10 Pro, officially comes with android 6 or 7 fw. There is also official Venz dualboot Librelec 8.0.2/Android 6 FW, which I have been using for sime time. I almost never botted into or used Android and decided to try Corelec 9.0.1 instead of LibreElec 8.0.2 (Kodi 17.3). I was satisfied with LibreElec it worked really great. After trying CoreElec 9.0.1 from SD card for a few days, which worked great, I decided to installtointernal cause I really don’t need Android, and thought I might be proficient enough to recover original firmware if I somehow managed to brick it. It went smoothly, installtointernal worked great for me. Scanning and refreshing libraries seems much faster.
My device uses Amlogic SOC S905X, it has 2/16 GB internal memory, and I used gxl_p212_2g DTB image.
Please don’t take this as encouragement, I’m describing my experience with specific device but it may not be the same for you. Take care and caution if you decide to install to internal, and be sure that you can restore your device into working conditions if anything goes wrong, before you attempt any of it.