I've been on 8.1.9 on 3020s, vm-300s, 820s, 850s, 220s with no issues. I believe that is the recommended support version.
Probably want to install the latest 8.0 version, reboot, download 8.1, download 8.1.9, install 8.1.9, reboot.
The upgrade path that @craigomatic already mentioned would be what I would follow. Keep an eye out for when 8.1.9-h4 actually hits recommended status so you're covered for the three vulnerabilities they announced Wednesday, by the time you upgrade 8.1.9-h4 might have actually had enough time to mature to reach a recommended status.
Update: I'm starting to get some weird behavior on my 800 series running 8.1.9, like management goes to 100% for an extended period of time, making the device unmanageable. Did I read about a memory leak? These have all been running > 30 days. I'm upgrading to 8.1.9-h4 immediately.
I didn't see anything about a memory leak in the list of addressed issues for 8.1.9-h4 in the release notes. There were fixes for memory or buffer leaks for previous versions of 8.1 though.
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