Catalyst's Shadow Spells is a fun secondary source book.
An adequate amount of content for the price, nothing revolutionary, and there are a few spells that first time storytellers should think carefully before allowing into their campaign (rot, petrify etc) but for a module to add some bang to your dry spell list, it serves its function. There are more listed traditions, but they all seem bland compared to the existing ones, there are a few that might pique the interest of someone who wants a pre-generated tradition that was not laid out in the Grimoire, and it provides some good flavor for the 6th World, but this will not make or break anyone's collect of SR5 pdfs.
Ultimately a fun buy for the mage of the group but ultimately missable.
[4 of 5 Stars!]