@SarahGen-- I think that both types work well, but the type with blades is a little bit easier to clean. The wires are very close together, which makes it more difficult to wash the blender when you're done. I can't say that the blades are super easy to clean, but it is relatively easier in comparison to the wires. They're both equally effective at blending however.
Aside from mashing potatoes, you can use the sharp end of a pastry blender to make indentations on breads and other baked goods. Unfortunately, a pastry blender is not a very multi-purpose tool. That's about all you can do with it. But it's cheap, so if you have room in your kitchen drawer and if you bake often, it's worth having on hand.