I voted days ago but dind't posted why.
SO, I choose invisible becuse visible has too much monsters in the path. Some blocking your way and it's kind of annoying, and in Hungry Cave there's a lot of visible monsters, I felt like an obligation to take care of all off them. And the Urzas are quite annoying.

Still a great feautre, I read in your blog Indy and Im looking foward to play MM1 and MM2 with the new features of MM3. ^^