I've never used these as I couldn't see their benefit at all, actually.

The water does evaporate, but is it at the same level as the plant's leaves (probably not) so that it would be useful? The evaporation rate is so slow that what does evaporate gets lost to the environment unless the space is really small and enclosed. I think humidity trays are one of the biggest orchid growing myths.



Your time is much better spent refilling the humidifier.