iPhone 4: Should I update to iOS 7?

So, in the title it says 'I', but really this is a question for my girlfriend.

I told her yesterday that Apple is releasing an iOS update today, and it is vastly changing the UI. She asked me if she should update, or leave it on iOS6.

Last year, for the iOS6 update, I told her not to update because she uses Google Maps regularly, so she held off until Google released its updated Maps app. Which worked out well, because Apple maps in my location was apparently horrible.

This year, the question is performance, will iOS7 run fluently on the iPhone4?

What is your opinion on this? I have heard mixed reviews about it being laggy and crippling the phone, is this true (and the blur effect isn't on apparently?)