We've been using Clearbit for about 6 months, and I'm very very happy with it. Best match rate and data completeness of the vendors we tested and affordable as you scale up with it.
The Marketo set up isn't too bad, especially if you've already gone through this rodeo once. Do be aware that they are a small team and, while very friendly, don't have the bandwidth for a ton of support if you have custom needs.
But I definitely recommend!
Can you provide details of where then data is coming from? Are they getting data from data providers or scrapping the web for publicly available data? or something else?
What is the legality of using the data in Europe, especially with GDPR coming soon?
What are the things of concerns with Clearbit vs other dndors like Demandbase, leadspace, etc ...?
Yes - it's fantastic.