The Echo series which this series spun off of was a lengthy, well developed set of novels that didn't shy from fleshing out characters and the lore of the world to establish a solid environment for the reader to dive into and come along for the ride. This series however, upon seeing it done, I am a bit sorry to say it doesn't hold a candle to its predecessor in the least. Where the first series was well crafted and drawn out, this one felt constantly rushed and short-changed from what it could have been in almost all ways.
The major context of the series is hastily touched upon in the beginning novel and even more briefly reviewed at the start of each follow-up, including this one, so if a reader wants any real in-depth look at other characters, the setting, and the build up to the events of the series, they would literally have to go read the Echo series to get the answers they seek, rather than finding them here. The character focus doesn't help this, as Kat Dubois is a very unstable narrator, not unreliable per se but unstable in that the feelings she embraces from scene to scene doesn't always match up with events properly. She is often a very frazzled, nervous, and overly stressed type of protagonist and it makes it hard to gauge any real outside feeling of what events are beyond the confines of her own head.
The other significant issue is the fact that these novels are barely that, just a bit longer than novellas each and altogether probably just equaling one, maybe two of the Echo books, if being very generous. Events are thus sped up to fit the length of the novels neatly and make them feel very bereft of more significant details, going from one thing to another in very quick order. Upon finishing each book so quickly I felt rather unsatisfied, like they were stopping just a quarter of the way in and were left unfinished from how they were. The feeling was the same with each, and up to this last book which instead left me with a rather disappointingly quick and tidy ending that didn't really feel like one. Not in the sense that the author is leaving the series open for an eventual return, but rather that the potential of it was left to sit on the cutting room floor.
Overall, while I still liked the characters and the world and lore, the way the series was handled made it feel like the author was trying to push the idea out onto the page as quick and easily as possible to get it out of her head and published to be done with it. Rather than a follow-up to the initial series, this just felt like a poorly done one-off spun off of it and stretched too far past its viable ability. I won't call it a bad book or a bad series overall, but I can't really say I'd recommend it to anyone who read and liked the Echo series, lest they feel the same lack of satisfaction as I have.