We are not selling the Maestro yet, you can only get it from M3D at present. But we're gradually updating the documentation to cover the Maestro in preparation for when we stock it. Meanwhile, the documentation for the Duet Ethernet is mostly the same as for the Maestro.
Thanks, you're right - it seems OK in Pronterface, so I can use that for hand-tuning the heater. Strange that only M307 seems to be affected, perhaps something to do with Octoprint's temperature polling.
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