1 W8.1 laptop - pretty stable but suboptimal on 1366x768 screen, fine docked with 24" monitor which is the apparent sweet spot (Desktop mode with large hi res monitor, physical kybd & mouse).
1 W8.1 SP3 - 4 installs before the keyboard would work reliably (neither onscreen or type cover). Buggy as hell, still has issues. The SP3 has been relegated to sacrificial beta box since I have alternatives for doing real work.
Refused the update on Surface 3, waiting for stability, likely 3-6 months.
Beware, The W10 Update wont stay hidden. Use Notify me of updates option and check carefully lest they slip W10 in on you. Hid the update, it came back in a week.