About a year ago I dealt with Nova Publishers. They publish scientific and often highly technical non-fiction. I figured I would take a few minutes and share my experiences with them.
I work as a research scientist, and got an email invitation from Nova to author a chapter for a book on a theme peripherally related to my area. I couldn't find anything here (I've been lurking for awhile) nor anything definitive on Preditors and Editors. I have a scientific book I would like published, and thought I could use this invitation as a test run to see what they are like to work with.
I responded, and was given a file of instructions to authors and a rather near deadline (about 10 weeks, which included Christmas and New Year's break!).
I wrote the chapter, but my workplace requires that all publications undergo internal review before being submitted to a publisher. I informed Nova of this, and told them that the chapter might be held up by this, especially as it is very hard to get anything reviewed during December. I was given a somewhat terse reply that said in effect "meet the deadline or we will proceed without you."
The deadline was not met, and they indeed proceeded without me. The book is currently at the printers, according to the publisher's website entry for that title.
My experience with them is not too unusual, I guess. However, there does seem to be have been some controversy surrounding this publisher and the quality of the work. See the Wikipedia article and references cited there (http://en.wikipedia.org/wiki/Nova_Science_Publishers). The controversy seems to have passed, and more recent input seems more positive. Looking through books related to my field, I see a mixture of contributors I know but mostly those I don't know from overseas.
Verdict: It seems to work for some people. I will not submit my non-fiction book to them, as I want it to sell for less than what comparable books sell for on their site.