What do you like best?
TheChecker was simple and straightforward, both in its pricing model and in actual use. We honestly did not even realize how valuable this service was until we had a specific use case; we will expand its use going forward. I also like their actual pricing as well as the way they price their service.
What do you dislike?
No real problems, though I guess their site can be a bit spare on documentation/explanation at times.
Recommendations to others considering the product:
This is a very specific solution to a very specific problem, so I'm not sure what advice you need other than TheChecker does a great job at validating email addresses. I have not used any of their competitors in anything other than a trial basis, but to us TheChecker stood out.
What problems are you solving with the product? What benefits have you realized?
The main problem we had was inheriting a very old, very large email database from a company we started working with to do email marketing. They wanted to email everyone on that list, but we knew if we did that it would be a disaster that could land us in spam jail. We were able to clean the list and remove a significant number of bad or questionable email addresses. We have continued to use it to clean other lists in more of a maintenance approach.