I directed my students to use Interactive Applet Skill Tests to supplement my freshman music theory online materials and keyboard activities. Most reacted favorably. Comments included "this helps a lot" and "good for practice". Of course, some found the material too hard while others thought it too easy.
Several students were not comfortable with the interface. I received comments such as "online work is tough and tedious" and "even if you know the right answer, the computer will sometimes count it wrong if it is not written in a specific way".