I read some articles about it but all where with a referal link, so i don`t really trust thoose articles. I need some other opinions.
I suggest that you visit bloggerhigh.com for a free alternative since SEO Pressor isn't cheap. It's not mine, but i'm using it and are very satisfied with it.
Yes it will help your SEO. Unlike ordinary SEO plugins, SEO Pressor and the one from Bloggerhigh will let you optimize all your posts with keyword density and so on. It will give you tips about what is missing in your posts too, like H1 tag etc.
Or you could just learn how to optimize your on-page. It's not that hard really, just learn it, and it becomes 2nd nature. Hope that helps.