This keyword research tool is effective, automatically providing you with keyword suggestions that other sites haven’t necessarily turned up (which it’s intended to do), along with their search volume, CPC, and Adwords competition. In order to get any actual information about the keywords, though, you need to upgrade to Keyword Tool Pro (which is a little misleading on the site copy). This plan is $88 a month, and if you’re just doing keyword research for Google, I’d recommend choosing one of the other tools for the price.
This keyword tool was built on a custom database we have compiled over the past four years. We researched data from the (now defunct) Google Search-Based Keyword Tool and also looked at a few more recent data snapshots to refresh the database and enhance our keyword coverage. Our database contains 28,527,279 keywords representing 13,762,942,253 monthly searches. Our database is primarily composed of English language keywords.
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).