Just finished 'Catalyst' an I thought it was OK. Nothing spectacular. Mostly it serves as a primmer on Jyn's early childhood, parents, their relationship with Krennic and some of the broad strokes of how the Death Star project developed.
Possibly the most interesting tid-bit is that the initial design didn't actually originate with the Geonosians, but was provided to them by Dooku, which means they probably came from Sidious. Could it actually be a recreation of an ancient Sith super-weapon? If not then who really came up with the concept?
There's also a little bit more kyber crystal lore. Mostly the idea that they're referred to as "living crystals". Something implied, though not make explicit in the Ahsoka novel. Also they're very clear on the point that synthesising them is impossible, since they grown in resonance with the living force.
Not exactly clear on the chronology. It seems to start a little after the second battle of Geonosis, with Jyn's birth ocurring about a year or so into the war and ending some years after the war, but when she was still very young. Four, maybe five at most? So not long after the events of 'Ahsoka' as it turns out.
Onward to Lost Stars. I'm pretty excited to read this one, hopefully it lives up to the hype.
Personally I was pleasantly surprised with 'Lost Stars', though some of that may have been due to low expectations. The way they advertised it as a YA romance novel put me off a bit and truth be told is very misleading. Yes the narrative follows the perspective of two people who do indeed become romantic, but that's not the sole focus of the narrative. It's more about how they change and grow over the years, both together and apart. The brushes with the familiar events of the movies are fairly well done and work organically within the story. Not cute or gimmicky like it very easily could have been.