I own a digital marketing agency and an EPS called Konvey. I'm very pleased with DataZapp's e-mail append service. The match rate was ~20% for my lists. The hard and soft bounce rate was very low and Feedback Loop complaints - a worry - were not an issue. Almost zero opt-outs and complaints. Way withing industry limits. My open rate was > 18% with a very soft initial contact on people who purchased our brand product 60 days ago.
There are lots of data management services one can choose from. Save your time and let this company demonstrated what they can do for you. We are very happy with the professional services provided by DataZapp. Their prices were very reasonable and their response time was fast. Our experience was exceptional. We highly recommend DataZapp!