The extend a shower was one of the best mods we ever did on our old trailer. Makes showering much more enjoyable and adds considerable room when extended out. Loved it. As a bonus, you can hang wet towels over it. I say go for it, you won't be sorry.
It replaced the old track and roller curtain system that was screwed to the ceiling. Filled the small screw holes with white caulk and you couldn't really see them. As to mounting, it depends on your situation. I was lucky enough to have studs on each end of the shower stall so I just used the supplied wood screws to go into the studs. Moly bolts or other anchors are fine too.