Their support is terrible. It took us over two weeks to get someone to answer basic questions such as: How are credits charged.
Which brings me to the second big issue. They charge you for every email they "identify". Whether it is 99% likely the email is correct or it is a not verified one. Basically, they charge you for a finger in the air guessed email.
The third issue was, even the 99% likely correct email addresses, showed a high bounce rate. After we started using an email verification tool, and run the "99%" emails through that system, we saw up to 40% of incorrect emails.
To put this in numbers: On average out of 100 people we were trying to get an email for, their system would provide us with about 45 "99% delivery rate" emails, about 15 "Strong Emails" and 40 "not recommended/not verified" emails. Of the 45 "99% delivery rate emails,", 40% were bad emails. That meant we got only 27 emails that were good too use, out of 100 we had to pay for.
So, if you have 5,000 credits per month, you get 1,350 good emails but have to pay for all 5,000 emails.
p.s. they recommend that you only use the "99% delivery rate" emails. Not sure why they then rate the second tier emails "Strong delivery Emails". Review collected by and hosted on G2.com.