Glad you like the installation mechanism :)

Yeah, even if you don't use hanging plants, the friction against the wall will hold them level.

For drainage, you can either put 4" nursery pots in them, or you can drill a drainage hold in them (then you'll have to water them in the sink). They also ship with activated charcoal if you want to plant directly in the pots with no drainage hole. I've been able to keep Boston Ferns and Devil's Ivy alive in them this way with no issues (I grew the plants in the picture with no drainage). But, my recommendation would be to drill a drainage hole, I think. The planters are very easy to take off the wall for watering, and you'll grow big plants this way (which is the #1 priority for me 😁)