With humidity rounding to the nearest 5% the API is effectively useless for automating any auxiliary dehumidifier. If my automation rule is “run dehumidifier when humidity is > 55% and stop when humidity is < 55%” this turns out to be a 6 point delta on average. Automation will run when humidity reaches 58% because its reported as 60 but wont turn off again until it reaches 52% which is reported as 50. A dehumidifier operating in quiet mode can take quite awhile to manage a 6 point swing and usually cant perform the job before the next AC cycle.
My automation will kick the dehumidifier off the next time the Nest reports cooling to save on electricity costs. However I still feel the API should be reflecting the same exact value that the Nest thermostat itself is reading to assist with more fine tuning of automation and possibly save on electrical costs in the long term.