Ok - here's my overview.
To start off I'd say that yes I will use the service again. I was making a list of new articles to be written before I posted this.
The quality of articles was great. Well researched and well written. I do like to go over my own articles and make modifications - but this gave me a really solid base to work with.
I'd say there were very few, if any grammatical errors. There may have been a "saying" or two that is not commonly used, but other than this it was pretty good. I had a really small unique niche selected - but the articles were written as if they had been in the industry for a while.
The turnaround time was a bit slow. I got my articles 4 days behind "schedule". I'd like to see this improved - or an improved estimate of how long the articles will take. I'd say take this into consideration, and order articles ahead of time.
Even with the time frame factor, this is a solid service for the price.
Good job.