Temperature measurement is not a problem. It doesn't need optimistic mode.
I have my DIY nodes that control heating in rooms (radiators). They are battery devices. Every 5 minutes they wake up to check if the switch (S_BINARY) is turned on or not. This switch requires optimistic mode.

I did as you advised. I deleted Mysensors in gui. I added the configuration in configuration.yaml. After rebooting HA still does not optimistic work. There is an entry in the log: 'optimistic option for mysensors is deprecated. Please remove optimistic from your configuration file '.
I'm afraid Home Assistant has killed the ability to use battery-operated MySensors devices.

Doesn't work.
Invalid config for [mysensors]: required key not provided @ data['mysensors']['gateways']. Got None. (See /config/configuration.yaml, line 175).
Gateways I have defined in the integrations UI.

Hi, the HOme Assistant documentation says that for MySensors integration you can set the 'optimistic' parameter. But how to do it? I have an MQTT gateway.

You have:
if (send(msg.set(fgehum)),true)

Should be:
if (send(msg.set(fgehum),true))

Regards
Marek L.

Works like a charm!