Author of Kill the Newsletter! here. Thank you for your comments! I didn’t know of NewsBlur and Feedbin and it’s nice to see that other tools take similar approaches to the use case. It validates that my solution was appropriate.
It’s unfortunate that NewsBlur and Feedbin bind the feature to their platform. But I guess it makes sense, Feedbin is even trying to make money. Anyway, whenever you need a free tool that doesn’t lock you in or ask for your personal information, I hope you consider Kill the Newsletter! an option :)