I'll start by pointing out that seeing "A Tale from the Canon of Tarn" leads one to believe it's a novel that takes place in the setting of an existing series, yet there is no series and this actually seems to be the author's first and, so far, only book. And then there's the fact that it's listed as having 456 pages, but only has the equivalent of about 150. So it's a good thing I picked it up when it was free, or I'd be feeling quite cheated.
Can't complain about the writing though, and it's also quite visual despite being so short, being filled with detailed descriptions that let the reader get a good idea about the part of the world that is presented. That's a tiny part, however, and most of the action takes place within a matter of hours, the rest being concentrated in a few brief but crucial moments that follow. So what is there is quite good, but there's far too little of it, and this also fails to provide enough of a chance to actually connect with the characters, or for them to develop in any meaningful way for that matter.
On that note, Dagger's powers and Anna's skills are a bit too much considering their age and lack of proper training, and the part that details fitting them with gear is quite odd, considering the circumstances. Also, quite a number of Dagger's actions and movements don't seem right, considering how he sees and knows things. Maybe not major issues in themselves, and maybe that also goes for the fact that the author seems to have been inspired to a fair extent by Temeraire, some themes from A Song of Ice and Fire, and probably also some other series I couldn't identify, or for the odd choice to include a sketch along with the description of the Dallanar Sun when it just has placeholders instead of the portraits and the tear at the center is not inverted, but, again, there just isn't enough content for the problems not to stand out.