Wlanman - that's fine. Feedback is not required, but we give you the option on every exam.
Pete, CWNP (like any exam vendor) controls the content. VUE (or Prometric, if an exam vendor utilizes their services; CWNP does not) controls the interface.
CWNP controls some other options like the aforementioned inability to "go back" or mark a question and return to it, the ability to comment or send feedback on a particular question, instant grading of the exam, etc.
As far as the VUE interface is concerned, it's pretty simple, and you get a tutorial before your exam (and that precious 90 minutes) begins.