Yes, it is. I subscribed last month, I'm unsubscribing this month. The searches are very UK oriented. It sucks.
I'm going to go with Keyword Discovery. I've been using SEO Book, Keyword Discovery, Wordze, and Wordtracker. I've been heavily using all of them, and hands down...the most accurate and logical is Keyword Discovery for me.
SEO Book is inflated, but it gives you a good idea of overall traffic. Wordtracker is months behind. I can't use it for any of the niches I'm in, it doesn't help me when I'm watching seasonal trends. Also....SEO book seems to use a yearly total and divide by that. Not good. Let's say you want keyword results for coats. It's stupid to put up content on coats in May because the results are just evenly divided. You need to know when the traffic is on an upswing. Keyword Discovery does that.
I'm not sure about the totals, but for very specific terms I've been using...Keyword Discovery (again) seems to be the most accurate. One specific term of mine is in the second position, and based on the traffic I get from it, KD looks like a monthly total.
I have no idea how they figure it out, but I don't sweat it. I've been in the lower positions but get a very high click through because I write killer meta descriptions. I make people want to click, I don't rely on just what position I'm in and a mathematical formula for it.
In my opinion, use the traffic as a base. Go to the 500 most search terms on the internet, do a search for that as a baseline....then compare your niche term against that. Hot or not. Traffic or none.