I checked your extension, I like the MEMO scanning feature.
My extension does the similar thing to yours (marking external links) but I thought whitelisting could be more effective but yes more difficult to maintain. But the idea is to try to also protect users that are on Busy.org or another official site or even if they do a google search and land on the scam site. At least if the extension recognizes it it will warn the user. Won't be perfect but one less victim is still worth it.