Visited one site on 22 November with sufficiently humanoid headers.
IP: 72.52.108.abc
UA: Mozilla/5.0 (compatible; DocSpotBot/1.0; +http://docspot.com/bot.html)
robots.txt: no
The URL given in the UA leads to an https redirect followed by a Firefox “insecure site” warning. I did not push on from there. IP is, I think, in one of those hopeless Verizon/Frontier/Fairpoint sprawls.