We at Moz custom-built the Keyword Explorer tool from the ground up to help streamline and improve how you discover and prioritize keywords. Keyword Explorer provides accurate monthly search volume data, an idea of how difficult it will be to rank for your keyword, estimated click-through rate, and a score representing your potential to rank. It also suggests related keywords for you to research. Because it cuts out a great deal of manual work and is free to try, we recommend starting there.
To be able to rank in the search engines is an art that must be understood and finding the right Keyword tool that fits into your comfort zone is a must. What I mean by ‘comfort zone’ is having a keyword tool that doesn’t confuse you before you begin even searching. Some go into far too much detail than is necessary. All you need really are good long tail ‘common sense’ keywords that other marketers may have missed.
Analyzing the current top 10 search results in Google is the most important part of keyword research. This is where you determine whether or not you can produce a webpage that can beat any or all of those results. The process is known as first page analysis – and it is by far the hardest process to understand and really figure out (especially when you first start out). Don’t worry though – Long Tail Pro has detailed and in-depth instructional videos available that show you exactly how to do this.

Most keyowrd databases consist of a small sample of the overall search universe. This means keyword databases tend to skew more toward commercial terms and the core/head industry terms, with slighlty less coverage of the midtail terms. Many rarely searched for longtail terms are not covered due to database size limitations & lack of commercial data around those terms. Plus if those terms were covered, there would be large sampling errors. Google generates over 2 trillion searches per year and claims 15% of their searches are unique. This means they generate searches for over 300 billion unique keywords each year. The good news about limited tail coverage is it means most any keyword we return data on is a keyword with some commercial value to it. And with Google's Rankbrain algorithm, if you rank well on core industry terms then your pages will often tend to rank well for other related tail keywords.
These are usually single-word keywords with insane amounts of search volume and competition (for example, “insurance” or “vitamins”). Because searcher intent is all over the place (someone searching for “insurance” might be looking for a car insurance quote, a list of life insurance companies or a definition of the word), Head Terms usually don’t convert very well.
The limit on manual keywords could be higher.  I personally wish we could input 10,000 keywords at a time, instead of 200.  However, I understand the costs that Long Tail Pro has to maintain each time a new manual keyword is input.  Not a deal breaker, I just wish the limit was higher. (To be fair, I don't think most keyword tools have a bulk manual option at all).