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!
I learned a lot from you and now make a couple hundreds per month in extra cash thanks to your advice. You provided us with great content and a great tool. I’m very happy for you. I have to say though that I’m sad you sold… customer service is so so so far and I know it’s cool for owners to sell subscriptions instead of selling it for a one time fee and I know it’s a new trend online but it’s really a trend I don’t like as a customer… Anyways. I’m very happy for you. Many thanks and congrats !!!

It would be great if you can provide comparative analysis of this tool with Google Keyword Planner. Since you’re using this tool so you can provide best comparison. One differentiation which I understood is that this tool works for yahoo and bing as well whereas Google keyword planner works only for Google but Google being a dominating search engine, gives the highest returns, so only this reason may not be enough to buy it.