my daughter is a slow reader (first grade) and my son is quicker but at his level (kindergarden) so I am going to use the workbooks over the summer since my kids like worksheets. I am not planning on getting the teacher guides either....and am going to order the books off rainbow research since it seems to have the lowest price.... can't answer your question but am following to hear what others say :)
I used it many years ago in public school and vaguely remember even looking at the manual. Some kids can fly through it - like seriously many, many pages a day. Some kids don't care for it as much or have a longer processing time.
For homeschooling, I did not pay for the manuals for Spellwell or WorldyWise... every so often there is something I'm not sure about but I figure it doesn't matter... a mistake might get made, we took our best guess, move on. I wouldn't mind having the WordlyWise tests, but not badly enough to pay for the teacher's manual to get them.