I love Email Hunter for the simple reason that it saves me so much time. Sure, there is a lot of software out there that does email validation, but here is why I love Email Hunter the most:
1) You search for a domain, and it tells you the best guess formula. You can then just apply this to ALL emails for people at that company, and boom, you're done with a group of people. Many other pieces of software ask you to search person by person, which is annoying.
2) Number 1 is useless unless there is data to back it up, and this is truly why I love Email Hunter. It will give you the formula, but the it will show you all the results, peoples names, emails, etc that are found all over the internet. It will link you to where that email was found, and it will tell you the date it was updated. This is invaluable because it may say email@example.com, but with a quick glance you can see that 10 of the results are indeed f.last, and they have 20+ sources anywhere on the internet. You know that formula is right at that point, and you can do that in a few seconds.
I'm not sure there is anything that I dislike. I use this for a very specific part in my process, and it performs the job it's intended to do perfectly.
Use this as your first line of defense for validation. It will save you time, it's easy to use, and it's mostly free. You only get something like 200 searches for free, but 1 search is for the domain so if you have 5 prospects per domain, you're getting 1000 email validations for free!
I'm validating emails as fast as I possibly can. I use Salestools.io to build a list, then I use Email Hunter as the first level of backup validation when Salestools doesn't find the email (which is often). This saves me a TON of time (and money because it takes my contractor less time).
Instead of searching through Google or using individual email validation tools per person, I do blocks by domain name through Email Hunter and I can find MOST emails. It's fast, easy, and frees up the time for me to do other work.