Working on it. Waiting for some packages.

The rectangular ones are slightly more reliable from personal experience but likely just as possible to be low quality. From working with them the design layout leaves less space to get obvious flaws such as the RH sensor being installed facing the board which seems to be true for most of the round ones, they also have a separate and dedicated temp sensor unlike the round ones and use a double battery setup since voltage can also affect the accuracy of the reading.

But the RH sensor between the units seem to be identical as is the inability to calibrate.

Personally the paper strips are very reliable if just looking for a binary answer of if it’s gotten past a threshold and are incredibly cheap.

Abe recommended an electronic daughter board sensor that was cheap but requires skills I don’t have.

And I have found medical grade ones that can be purchased cheap “used” as they are often single use for shipping purposes to make sure the item was kept in specific conditions. But that brings me back to waiting for the. To arrive and test.

TL;DR

These cheap electric square or circle ones are both luck based with some preference to the square. But cheap paper humidity sensors can be gotten if you just want to toss them in a bag to make sure they haven’t gotten water damaged as a binary identifier.

For reliable accuracy look elsewhere.