Disk sanders are the ideal choice for sanding small parts. The rotating disk is less likely to pull the workpiece out of your hand than a sanding belt, and it takes up less floorspace. Sanding the ends of boards is also easier to do on disk sander, than it is on a belt sander.
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It's best to limit the disk sander to smaller parts. Trying to make it do edge or even belt sander work is not really an option. Shop for a machine that provides enough capacity for your small part needs, and purchase an edge sander for everything else.