Purchased from DriveThru RPG on a sale because it looked like an interesting concept. One of the first third-party, small publisher print books that I have purchased. In short, this is worth keeping and will remain on my shelf - if only because I only paid $15 for it.
What the Ebonclad setting does well is provide a template and some solid ideas for the concept of a Thieves Guild in a fantasy TTRPG. It also offers some interesting "canned" adventure concepts for use in such a setting, either independently or chained as a campaign.
What this book does not do well is believable worldbuilding within the setting that the author has constructed. I would certainly never use the city of Kintala as a setting. As presented, this immensely powerful thieves' guild is much too omnipotent in a city of 14,000 - In my opinion, this would work much better spread over a considerably larger setting or group of large (larger!) cities in order to really offer the mechanics the scale at which they seem intended to operate.
Still, a pretty well-crafted supplement/adventure toolkit for what it is. Will stay on the shelf and hopefully contribute to future concepts.