According to the documentation for http://simple-press.com:
Note that this plugin is big! Use a reliable tool to upload it to your server. Please note that FileZilla often fails or corrupt files during upload. Please avoid using it.
I'm completely unaware of anything like this. Is it true, and if so, what's better (on OSX)?
mac ftp
yields Transmit, Cyberduck and Fetch on page 1, which are, AFAICT, the most popular OS X FTP clients, as well as Yummy FTP (I don't like it, YMMV) and Interarchy. Let's focus on the part regarding FileZilla reliability, not on alternatives. That's the easy part.