Here is the ahrefs.com bot UA:
Mozilla/5.0 (compatible; AhrefsBot/5.2; +http://ahrefs.com/robot/)
I did some research here, and so for now I've allowed the bot as I run ads. However it's hitting my site at around 50,000 per week.
Is it wise to put delays in the robots.txt or even just block it completely? Please advise. Thanks!