I think most of the issues mentioned can be attributed to the attached.
I find with mine that it does rattle when shaken, depends on just how you want the result, I actually prefer "over ice but not shaken", I really hate that rattling noise in my 70-200.
When attached to your Camera Body you may find some mild to serious issues with weather sealing.
Attachment does cause light leak issues except when used in the dark.
Only real downside on mine is the Zoom Rings are very very difficult to Zoom with,
I can't speak for others of course, but I can say that mine does produce an amazingly good Cappuccino just when you need it, about dawn in the Okavango Delta.