OK I gotta ask: these 2 particular bots constantly scan my site once an hour. Why?
That is what they sell back to users, presumably. I am actually quite interested to see how clear their data / recommendations would be, but haven't had the time to do so yet.
I have tried both, and while ahrefs probably has a better dataset, semrush does very specific recommendations when it comes to link building for example. They will suggest what sites to contact to ask for backlinks (something I have not yet tried, because other people email me all the time asking for backlinks or guest posts so I know how annoying it is).
One thing you can do is stop them from scanning your site with robots.txt – some SEO people recommend this to prevent your competitors from finding out where you got your backlinks from, but I haven’t tried it.