Well, after a little more experience with these things, they appear to
work fine if you're dealing with a medium like soil. They worked
fine, for example, with other plants rooted in regular potting soil.

However, while the one in the Cymbidium pot that has not been repotted
in a while still appears to be working adequately, the other one is
not satisfactory. With the plant that has been repotted recently (I
can tell because the medium is so loose and coarse), there are two,
opposite problems. On the one hand, the neck of the globe easily gets
plugged, and this results in no water being delivered. On the other
hand, when you make certain the neck is not plugged, the water drains
out quickly.

In short, these aqua globes appear to be fine with soil, and in
nurturing those orchids where the medium is degraded to the point the
plant ought to be repotted as soon as practicable (e.g. after the
current blooms have faded, or when new growth appears, whatever the
best guidance is for the orchid in question), but with most media that
are suitable for orchids, it is just too coarse for aqua globes to
work as intended.

If one wants that kind of convenience, I suppose one would have to set
up probes to measure water content in the media, feeding that data to
a computer which would provide water automatically once the medium
dries to some programmable level.

Cheers,

Ted