Don't see why this has to be an either or question.
- A blade that sticks and then skips along your face when shaving. Possible for both DE and SE razors though most commonly mentioned as an issue for SE razors, especially when shaving against the grain (ATG) where this can cause a nasty cut. I've seen lots of mention of this definition both in recent on-line materials in shaving "how-to" documents that go back over 100 years.
- A blade that flexes (or vibrates) during the shave. Have seen even more posts referencing this from many sources including B&B members that related it to shaving noise level to marketing materials for various razors touting superior blade clamping. I've even seen a patent that reference reduced blade chatter though it provides no proof or statistics.
Is there a reason to arbitrarily split these two things? They seem like a spectrum of the same thing. If the blade flexes it can make noise, if it flexes too much, it can also bite you and give nicks. I have a lot more confidence in using my razors which provide a rigid blade edge. The only razor I do not feel secure with are my Super Speeds. I can shave with them, but they do not have the rigidity of most other razors in my den.