How acceptable are the outputs of automatic LaTeX converters for journals with LaTeX requirement? Is there anybody there, who uses this combination as the pipeline of document production in his/her work? IF so what are the common bugs/imperfection that one should expect. 

From a latex-noob point of view, it seems faster and easier to work(collaborate) on a paper in Microsoft Word (For months) and then use a plugin or some other quick converter to make it into a latex on the last week(ideally a day) if there exist a smooth conversion tool to get to .tex format?

a reliable/acceptable converting should address the journal template/format, tables, table of content, footnotes, margins, figures, equations and bibliography. Is there a bulletproof conversion out there, and if not why?
The most probable answer to what acceptable is the conversion from word to LaTeX is probable too little. The main reason is that word is more based in local format (visual appeareance) rather than semantic tags. 

For instance, you need to specify that a group of specific paragraphs are the abstract. LaTeX made this using an instruction like 
\abstract{ ... text ...}. A converter needs to look in styles to learn the meaning of the text fragment against its list of heading, leyends, abstract, section, subsection, etc.

But if what you want is have a simpler medium to wrote and rewrote contributions to the text, provided that you have a a solution to create graphics in jpg, png or pdf format and a transfer the more complex tables to LaTeX way, you can use Pandoc to convert from word to LaTeX.