Motorized small diameter drums are a big helper for inside curves. A dedicated spindle sander can do the job well while keeping angles perfect. This unit has the flexibility of getting inside those pesky curves and the convenience if bringing the tool to the work, however keeping angles is much more difficult. Kind of like using a ROS on board ends.
Either way, useful tool for a lot of stuff. Easy to make one with just a drum sander "balloon" arbor and handle but having a properly built unit is a time saver.