It not being open source is a political argument, not a technical one.
EDIT: I ended up doing just that. It took roughly 5 minutes (most of that was making sure I had my PATH for Java set up correctly on this machine) to get decompiled Java code ready to inspect.
If I can compare the open source to the reverse engineered code to see what I'm really using/getting, that seems like a technical advantage. Also, all of the reverse engineered code I've worked with has been difficult and time consuming to digest (missing var names, comments etc); open source gives me a technical advantage in analyzing and understanding the code. Lastly, looking at a companies open source lets me assess their technical sophistication and practices which also seems like a technical advantage.
I haven't spent much time thinking on this subject, but the political aspect seems to be the line of thinking that says: you will engender trust by making a project open source.
Is your reasoning similar?
Also are there good tools for reverse engineering iOS deployments?
There are many; since apps are native on iOS a standard disassembler would work. But there are many more specialized tools, such as class-dump and Hopper.
I'm not an Apple consumer, I don't know anything about iOS in particular.
My point is open sourced code is much more readable and hence more accessible and you can build it yourself and use it most of the times.