The library and crawl index for Ahrefs is unparalleled. If you need to know competitive landscape and build backlinks, there is not another player in this space. moz, etc doesn't come anywhere close. they do alright in other factors, but purely from a research and backlink profile perspective Ahrefs is the leader without competition. Comparison features and backlink tracking are indispensable. Good to help with estimation of traffic on potential client's websites. You can go to the table in a client meeting better prepared. This along with SEO powersuite makes a good package.
Depending on the plan, you are only allowed up to 100 domain searches a day. If you purchase their top tier plan you only get double of that. Sometimes it can take you several days to do certain types of research. This can start to get a little bothersome as we work with several clients and all of them need to use this software to make sure everyone is getting the best work that we have to offer.