Best SEO tool you've paid for (besides this one)?

Always interested in what people use alongside ours. Ahrefs, Semrush, Screaming Frog, something niche? What does it do that nothing else does?

Say what the tool does well, what it costs, and the one job you would not want to do without it. Honest downsides help too. Free tools such as Search Console and the Rich Results Test count as well if they are part of your routine.