Weaknesses: There's a LOT going on in this 400 page book, and some of it is not well explained. I never felt very sure about what Sal's father was trying to accomplish, or about how Sal brought things from other universes. Gabi has a lot of "dads" with really odd names (e.g. Grizzly Dad'ums), and that was never made clear, nor was the existence of a robot/android character. The plot is a bit hard to discern with all of these wacky goings-on.
Sal and Gabi Fix the Universe is due in March 2020, so this is going to be a series. It's part of the Riock Riordan presents line and is similar to Margot and Mateo Save the World by Darcy Miller, Holms' The Thirteenth Goldfish, and Downey's The Ninja Librarians.