The primary difference is that Long Tail Pro is a big time saver over MS. With Long Tail Pro you are able to enter in multiple seed keywords at once (rather than just 1 with MS). So, instead of entering in 1 seed keyword, waiting five minutes, then going back and entering in one more; you can enter 5 seed keywords (for example), hit generate and then see all the keyword ideas at once!
3) KWFinder is one of the "newer" kids on the block, but it's probably just about the easiest way I have found to find new long-tail keywords quickly. A couple of things I like about this tool is that it allows me to create lists of keywords. So I can group up my different sites by lists and revisit them at a later date. I can export the data to CSV and start building out campaigns. It also keeps a nice scrolling list of the last 20+ keywords you have looked up. The SEO difficulty indicator comes in very handy as well! As far as ease of use goes, KWFinder wins hands down.
Using the good ol' free Google Keyword Planner is great. But there is an alternate universe of Long Tail keyword phrases that live in Google's other database--namely, their "Autocomplete database." That's the database that is accessed when you're typing queries into the Google search box (notice that list of suggested keywords that pop up as you type?)
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Long tail keywords can find people who are later in the buying cycle, and more ready to buy. For example, somebody searching for “tents” is probably early in the buying cycle, just starting to research what they want. Whereas somebody who searches for “North Face Kaiju 4 person tent” already knows what they want, and is more likely to be ready to buy.
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Keyword everywhere is another useful keyword tool. You can install it on either Firefox or Google Chrome. The tool will be able to show you competition data, cost per click, and Google Keyword search volume of multiple websites and keywords. This free extension can help you to save a lot of time. It can assist you to find long-tail phrases including their precise search volume, competition data, and CPC.
The link back to googles API is crap – it keeps coming up with password authentication which renders it virtually useless when trying to find your own rank. Sells you the software initially. But then tries to sell you a load of stuff afterwards which effectively tells you the first version you have already paid for is useless without the extra “bonuses”. Not a nice way of doing business
In a nutshell, Long Tail Pro helps you quickly find keywords in bulk based on a seed keyword that you input.  In addition to returning hundreds of related keywords, the tool also shows search volume (monthly search volume), advertiser bid, number of words, rank value, and my favorite Keyword Competitiveness (helps you judge the competition and keyword difficulty).