We slowly need to interface with an app at work that uses fixed-width too. It does not sound that bad if you hear it but it sucks to figure out where you are missing whitespace when most fields are not used and therefore all whitespace. Oh, and of course there are a lot of fields, also are aligned/formatted differently based on their type and has thin/no/wrong documentation. And I have yet to find a simple but decent “debugger”.
I would like to point out that they are free to modify the source code before building the binary they distribute. Being open source does not mean protection from secretly stealing data.
With chrome it is obvious because the closed part is called chrome and the open is chromium. But it is certainly possible to not make “stealing” magic on top public.