The pots are not undrained, they actually have two holes about and inch from the bottom. This keeps water/fertilizer in the reservoir. When you water, you flush the pots which keeps a fresh supply of water and fertilizer for the plant. The leca wicks moisture so the roots are kept as moist or as dry as the plant prefers.
I prefer to grow this way, it's easier to water, the leca is reusable and I don't have to deal with gnats or organic potting media.
Here is a link you might be interest in:
How to pot an Orchid using the Semi-Hydroponic method.
Joann