We have been immensely blessed in the past 2 decades with first year Grammar books (Mounce, Black), yet they are both 20+ years old, and have their own individual teaching styles. What Decker offers is a new face, fresh voice, and distinct style. I highly recommend both Mounce and Black, but this new book should not be ignored, and would make a great companion to one of the other volumes, if not a primary.
You can visit Rod's blog here. It contains a lot of interesting and helpful information from years past.
His grammar can be purchased here.