Writeseed is a good tool for writing content.

But I feel the lack of functionality with a feature. This is hampering me to get the most out of this tool.

There is no option to manually add keywords to the "SEO research & full-length article" feature. This feature suggests some good keywords which are good but it also should have let us input some keywords manually to optimize the article based on those manual keywords too.

I reached out to them. They told me that they would add this functionality.

Will edit this to 5 stars, after the feature has been implemented.
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1st edit:
They implemented the feature, So it's 5 stars now.