I'm not familiar with the GSA email scraper. But I have done a little bit of scraping with scrapebox. Works pretty well, but my team ended up making a custom scraper that we use in projects.
Scrapebox works like this: Put in your keywords, and then use the keyword scraper tool to expand that list.
Say you want to scrape site that do computer repair.
You would go into the SB Keyword scraper and type "computer repair and let it scrape 150+ keywords. Then remove duplicates. Then copy/paste those results back into the left pane and run it again. Remove duplicates. You should have 2000+ keywords. Put those in your main kw list.
Select your custom footprint at the top (or leave blank). I like to use: "intitle:" to make the list targeted for the keywords much better.
Be sure to use proxies btw.. and scrape away.
After harvesting completed, use the "email grabber" to capture emails from the sites.
Be careful..as there will likely be spamtraps on those pages...