Plumbing with flex clear hose vs copper.

I was at a friends last night helping w/ some plumbing and the contractor who plumbed his new bathroom used a flexible hose instead of copper to run in walls from the basement to the upstairs. I guess it's similar to the yellow flex hose used in gas now, except this is for water. I saw in the basement how the flex was tapped into copper but couldn't figure out how or what was used. Is this good practice and material or is copper still better?

Clear clear, or sort of milky transluscent clear? If sort of transluscent, it's just PEX; getting to be the new standard material. Do a search here & you'll find a lot of info on it.

I can't tell you much about it, I've only seen it 3-4 times & never worked with it yet. Others here have, just wait a bit & they'll drop by with more...