Digital Heaven has a solid reputation for FCP plugs - and at $10 per unit you really can't go wrong. The ones I've used are excellent.
What the dropout filter lets you do is replace a section of a damaged field with the previous (or next, or other) field. So, no messing around in AE. You can do this yourself in FCP, but the filter makes it a lot faster and more precise.
There's a bunch of good simple tutorials and a free demo here
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