Are those doors usually open all at the same time??? That seems kinda crazy.
Also it’s not about “locks” on these doors. People usually know you’re in there. It’s that there is no odor or sonic blockage. There’s usually a decent gap between the door and wall.
So for anything other than the least offensive tinkles or BMs, it just feels wide open.
They are so clever. 
This is why I love my job. Our forums get the real talk out to the world. Woot! Deals & Shenanigans & Nostril Protection.
Since all your buying is the hardware you can use a solid core door and use exterior paint for exterior spar varnish on the door and it’ll be fine
I have a very important question. I want to use 2 13 ft bars and hang a 13 ft barn door using all 4 hanging rollers on that 1 door for under my deck. Can I install or weld 2 13 ft bars together and have the 13 ft door slide smoothly between bars? this is to completely close off the underneath of the deck and then completely open it up when I want to drive my truck under there. If I can extend the bars then I would be getting 4 of these bad boys!
Man there is a lot of snark on here.
When people say they are using these for their bathroom doors, it is almost always for the master bathroom which should also contain the toilet in its own little room with a real door and fan. The barn door is perfect when you want to block the light in the bathroom or want some privacy. It is never meant to be blocking sound.
Most new construction homes tend to have the master bathroom open to the bedroom. No physical door. A barn door makes an aesthetically pleasing solution. And no, it is not the same look as a pocket door.