Although at least one cost me several yards on a tee shot, I like them, as I don't even have to bother looking for a sprinklerhead when they're around, and I notice a lot of others don't either. Once you see that reference point, you're ready to go.
Visually, I think if they're done right they don't detract at all. Just a nice, classy, black and white post about three feet off the ground. Flat markers to me are usually worthless as they require incessant walking around, and if they don't, they're usually too big and are therefore more visually distracting and gawdy than a simple 150-pole.