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).
Google prefers to not share long tail searches in this tool – because the tool is designed for Google Adwords advertisers. If advertisers bid on those long tails – they would have less competition and therefore pay less for the Adword, and therefore Google would make less money e.g. bidding on the term weight loss for girls under 18 is cheaper than weight loss.
Keyword Researcher is designed to search the Autocomplete databases of Google, YouTube, and even Amazon.com. That's a lot of keyword sources! As you probably know, if you're building an authority site, or if you would like to become a dominant player in your niche, then starting with a large database of keywords (that your customers are actually typing in) is a powerful marketing tool.
This makes Google Suggest a relevant source for keyword research, it contains a large amount of organic keywords very closely related to a full or partial keyword and can be used to find additional most searched appending keywords that make the whole keyword less competitive. Google Suggest can be researched through the Google Search website or through a compatible browser for a small amount of keywords but also in large scale using free scraper tools.
This is a rather crude metric because it presumes one can monetize all the traffic they receive AND one can generate as much profit per visitor as Google does. Anyone who could do both of those would likely displace Google as the first consumer destination in their market (like how many people in the United States start ecommerce searches on Amazon.com rather than Google.com).