Same story for me. First attempt got my Mars stuck in a boot loop, second one worked fine. I haven't noticed many differences so far - on the positive side, the boot time is definitely faster. The battery usage is the same, I don't see any difference.
On the negative side, after reinstalling all my apps I have my Perfect Viewer crashing a lot (never crashed before on Android 6). Haven't root caused it though, so it might not be related to Android 8. I'll post an update once/if I can root cause the crash
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