I think they are great as long as they have an appropriate fit for the lesson. There are many pros such as student engagement, dynamic user interface, hands on tactile and visual learning, individual pacing, and sharing ability. As a high school teacher, apps such as Geometry Pad or Fluid Math are great for exploration. Geometry Pad is similar to the Geometers Sketchpad software for computer. With this app, you are able to explore geometric theorems and concepts with your finger and an Pad as the tool rather then a compass and straightedge.
With the FluidMath app, you are able to write out equations, and see a graph as you would see with a graphing calculator, the difference being, you are doing it all with your finger. You can easily see transformations and the effects of coefficients on the graphs. So far I'm aware of linear, quadratic, logarithmic, trigonometric, and absolute value functions in the app.
I feel cons would be the teachers comfort level and experience with using the technology. Scaffolding might need to be put in place for students that need more assistance using the technology or app. Cons could also be that the technology may fail or equipment could be damaged in this case a plan B must be necessary such as working with partners or using an alternate computer software program.
To maximize the learning, I would definitely have a plan and a set of goals I would want my students to achieve such as what essential questions or objectives do I want my students to accomplish today. Technology for technology sake is not a reason, there must be a need for using the app that will help student learning. The culture of the classroom must be established so that rules and guidelines must be followed if students will have the privilege of using mobile apps in the classroom. The lesson plan should include steps to take if students don't follow directions as well as further extending/exploring for advanced students. I would also have some established time constraints for using the apps to keep students attention and be able refocus and explain when appropriate.
There are a lot of great math apps out there, as a teacher, I would make sure you have a plan in place of where the app or apps you wish to use will work in the lesson. I would make sure your addressing the standards and choosing quality apps that will encourage critical thinking as well as creating with mathematical concepts.