It's a great software. I used the free version for a big period now, and I'm very satisfied. I will probably buy the professional version later this day.
Please always look at the expanded features. Sometimes the investment for better/upgraded software is not always worth it. Check your needs, and what the professional version offers, and make a decision from that view.
I use Web CEO Pro edition and love it. I really get a lot of use out of the customized ranking reports. I generate ranking reports on a monthly basis for my SEO clients and it is so easy to send a branded report directly to them via email.
I was lucky enough to purchase it when they were running their promotions. I got it for like $270.