2 unrelated questions: rock wool and plant walls

[camille1585]

I'm seeing these two things over and over again on the french orchid forum, and I don't know what to think of them.
First, a lot of people swear by rock wool as a medium for their orchids. Is this a good idea? From what I know, if it dries out it acts like a sponge and pumps water out of the orchid roots, and I think salt buildup might be a problem. pH and conductivity have to be constantly monitored from what I read.

The second thing is a plant wall. Orchids are mounted on a felt-like fabric and water drips from the top every 5 minutes to water them. The unused water drips into a tank, and then is recirculated with a pump. The final thing looks so cool and saves a lot of space, but I would be really worried about spreading diseases! Any one have experience with this?