We don't use them in our service because we find that people tend to get a little too trusting of the software and mistakes are made. Different sites name fields differently, and sometimes the form filler puts data in the wrong fields.
When you're building citations all day every day, it's easy to miss these little mistakes that the form filler software makes. The time we spend trying to really carefully review the info input by the form filler is about the same as if we just did manual copy pasting, and we see less mistakes with the manual method.
Our triple check (including software check) catches all of our mistakes with citations, which allows us to use Last Pass. If you don't have a good check system in place, you may not want to use one as Darren mentioned.
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