If you already like the Iron Druid series and have read them all, this will make a pleasant diversion from the tedium of waiting for more. It's nice to have a little more perspective on some magical elements of the series universe. Oberon's a hoot. But, like <I>The Lone Gunmen</i> spinoff of <I>The X-Files</i> in the 1990s, it's not likely to make fans out of newbs or win fallen-away fans back.
I got the eARC from NetGalley ages and ages ago and finally finished the read after more than a year of neglect. In fact I was surprised to find it on my Kindle...and I guess that's everything you need to know right there.