I run 6 and it's been updated again last month. I haven't had any problems. Here's the update info
SHIELD TABLET K1 SOFTWARE UPGRADE 1.2
04/13/16
This update for SHIELD tablet K1 contains important system enhancements & bug fixes, including:
Supports the new Vulkan™ API for high-efficiency access to SHIELD’s graphics hardware
Adds Android 6.0.1 changes
- Repositioned Navigation Buttons in Landscape mode & Updated Emojis
- Double Tap Power Button to launch SHIELD Camera app
- Do Not Disturb Until Next Alarm
Support for Android Doze mode & additional power optimizations
Adds USB MIDI support
Adds memory compression enhancement
Improved Wi-Fi connectivity when waking from sleep
Fixed Compass functionality
Fixed Gamepad Mapper issues
Fixed issues with moving apps to SD card
Fixed Doom 3 HDMI output issue
Repositioned Lasso Capture icons in landscape mode
Update to Android 6.0 Security Patch Level March 1, 2016
Overall stability and security enhancements
Then here's the link to top it off -
Support