It's a great Acquihire. Uber immediately gets all this self-driving expertise.
Uber already has plenty with its ATC in Pittsburgh (the core engineers were hired from CMU's robotics lab). I'm guessing Otto has expertise specific to the trucking domain. At supposedly $680M, it seems like a high price.
It's former Google self-driving car engineers so they have a lot more than a few months of knowledge about the domain.
The Bloomberg article claims that they left Google to bring their product to market more quickly.